[libcamera-devel] [PATCH 8/8] utils: ipc: Update mojo

Milan Zamazal mzamazal at redhat.com
Fri Jan 5 14:04:37 CET 2024


Laurent Pinchart <laurent.pinchart at ideasonboard.com> writes:

> Update mojo from commit
>
> 9be4263648d7d1a04bb78be75df53f56449a5e3a "Updating trunk VERSION from 6225.0 to 6226.0"
>
> from the Chromium repository.

I don't know which one but when fetching the required components from
chromium.googlesource.com manually and applying update-mojo.sh, I get the same
tree.  I also checked it compiles in my environment, where it previously failed
due to the Python incompatibilities.  So the change looks all right to me.
Thank you for fixing this.

> The update-mojo.sh script was used for this update.
>
> Bug: https://bugs.libcamera.org/show_bug.cgi?id=206
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

Reviewed-by: Milan Zamazal <mzamazal at redhat.com>

> ---
>  utils/ipc/mojo/README                         |   2 +-
>  utils/ipc/mojo/public/LICENSE                 |   2 +-
>  utils/ipc/mojo/public/tools/BUILD.gn          |   8 +-
>  utils/ipc/mojo/public/tools/bindings/BUILD.gn |  36 +-
>  .../ipc/mojo/public/tools/bindings/README.md  | 239 +++--
>  .../public/tools/bindings/checks/__init__.py  |   0
>  .../bindings/checks/mojom_attributes_check.py | 170 ++++
>  .../checks/mojom_attributes_check_unittest.py | 194 ++++
>  .../checks/mojom_definitions_check.py         |  34 +
>  .../checks/mojom_interface_feature_check.py   |  62 ++
>  .../mojom_interface_feature_check_unittest.py | 173 ++++
>  .../checks/mojom_restrictions_check.py        | 102 +++
>  .../mojom_restrictions_checks_unittest.py     | 254 ++++++
>  .../chromium_bindings_configuration.gni       |  51 --
>  .../tools/bindings/compile_typescript.py      |  27 -
>  .../tools/bindings/concatenate-files.py       |   5 +-
>  ...concatenate_and_replace_closure_exports.py |  10 +-
>  .../bindings/format_typemap_generator_args.py |  36 -
>  .../tools/bindings/gen_data_files_list.py     |   2 +-
>  .../tools/bindings/generate_type_mappings.py  |   4 +-
>  .../tools/bindings/minify_with_terser.py      |  47 +
>  .../ipc/mojo/public/tools/bindings/mojom.gni  | 853 ++++++++++--------
>  .../bindings/mojom_bindings_generator.py      |  62 +-
>  .../mojom_bindings_generator_unittest.py      |   6 +-
>  .../tools/bindings/mojom_types_downgrader.py  | 119 ---
>  .../tools/bindings/validate_typemap_config.py |   5 +-
>  utils/ipc/mojo/public/tools/mojom/BUILD.gn    |  18 +
>  .../mojom/check_stable_mojom_compatibility.py |  69 +-
>  ...eck_stable_mojom_compatibility_unittest.py |  87 +-
>  .../mojo/public/tools/mojom/const_unittest.py |   2 +-
>  .../mojo/public/tools/mojom/enum_unittest.py  |  30 +-
>  .../public/tools/mojom/feature_unittest.py    |  84 ++
>  .../mojo/public/tools/mojom/mojom/BUILD.gn    |   3 +-
>  .../mojo/public/tools/mojom/mojom/error.py    |   2 +-
>  .../mojo/public/tools/mojom/mojom/fileutil.py |   3 +-
>  .../tools/mojom/mojom/fileutil_unittest.py    |   7 +-
>  .../tools/mojom/mojom/generate/check.py       |  26 +
>  .../mojom/mojom/generate/constant_resolver.py |  93 --
>  .../tools/mojom/mojom/generate/generator.py   |  11 +-
>  .../mojom/generate/generator_unittest.py      |   9 +-
>  .../tools/mojom/mojom/generate/module.py      | 783 +++++++++++-----
>  .../mojom/mojom/generate/module_unittest.py   |   2 +-
>  .../public/tools/mojom/mojom/generate/pack.py | 151 +++-
>  .../mojom/mojom/generate/pack_unittest.py     |  30 +-
>  .../mojom/mojom/generate/template_expander.py |   2 +-
>  .../tools/mojom/mojom/generate/translate.py   | 464 +++++++++-
>  .../mojom/generate/translate_unittest.py      |  82 +-
>  .../public/tools/mojom/mojom/parse/ast.py     | 145 +--
>  .../tools/mojom/mojom/parse/ast_unittest.py   |  12 +-
>  .../mojom/mojom/parse/conditional_features.py |  21 +-
>  .../parse/conditional_features_unittest.py    | 155 +++-
>  .../public/tools/mojom/mojom/parse/lexer.py   |   8 +-
>  .../tools/mojom/mojom/parse/lexer_unittest.py |  10 +-
>  .../public/tools/mojom/mojom/parse/parser.py  | 108 ++-
>  .../mojom/mojom/parse/parser_unittest.py      |  39 +-
>  .../mojo/public/tools/mojom/mojom_parser.py   | 119 ++-
>  .../tools/mojom/mojom_parser_test_case.py     |   6 +-
>  .../tools/mojom/mojom_parser_unittest.py      |  31 +-
>  .../tools/mojom/stable_attribute_unittest.py  |   2 +-
>  .../mojo/public/tools/mojom/union_unittest.py |  44 +
>  .../mojom/version_compatibility_unittest.py   |  73 +-
>  .../public/tools/run_all_python_unittests.py  |   8 +-
>  utils/ipc/tools/README                        |   2 +-
>  utils/ipc/tools/diagnosis/crbug_1001171.py    |   2 +-
>  64 files changed, 3830 insertions(+), 1416 deletions(-)
>  create mode 100644 utils/ipc/mojo/public/tools/bindings/checks/__init__.py
>  create mode 100644 utils/ipc/mojo/public/tools/bindings/checks/mojom_attributes_check.py
>  create mode 100644 utils/ipc/mojo/public/tools/bindings/checks/mojom_attributes_check_unittest.py
>  create mode 100644 utils/ipc/mojo/public/tools/bindings/checks/mojom_definitions_check.py
>  create mode 100644 utils/ipc/mojo/public/tools/bindings/checks/mojom_interface_feature_check.py
>  create mode 100644 utils/ipc/mojo/public/tools/bindings/checks/mojom_interface_feature_check_unittest.py
>  create mode 100644 utils/ipc/mojo/public/tools/bindings/checks/mojom_restrictions_check.py
>  create mode 100644 utils/ipc/mojo/public/tools/bindings/checks/mojom_restrictions_checks_unittest.py
>  delete mode 100644 utils/ipc/mojo/public/tools/bindings/chromium_bindings_configuration.gni
>  delete mode 100644 utils/ipc/mojo/public/tools/bindings/compile_typescript.py
>  delete mode 100755 utils/ipc/mojo/public/tools/bindings/format_typemap_generator_args.py
>  create mode 100755 utils/ipc/mojo/public/tools/bindings/minify_with_terser.py
>  delete mode 100755 utils/ipc/mojo/public/tools/bindings/mojom_types_downgrader.py
>  create mode 100644 utils/ipc/mojo/public/tools/mojom/BUILD.gn
>  create mode 100644 utils/ipc/mojo/public/tools/mojom/feature_unittest.py
>  create mode 100644 utils/ipc/mojo/public/tools/mojom/mojom/generate/check.py
>  delete mode 100644 utils/ipc/mojo/public/tools/mojom/mojom/generate/constant_resolver.py
>  create mode 100644 utils/ipc/mojo/public/tools/mojom/union_unittest.py
>
> diff --git a/utils/ipc/mojo/README b/utils/ipc/mojo/README
> index d5c24fc3b5cb..961cabd222e3 100644
> --- a/utils/ipc/mojo/README
> +++ b/utils/ipc/mojo/README
> @@ -1,4 +1,4 @@
>  # SPDX-License-Identifier: CC0-1.0
>  
> -Files in this directory are imported from 9c138d992bfc of Chromium. Do not
> +Files in this directory are imported from 9be4263648d7 of Chromium. Do not
>  modify them manually.
> diff --git a/utils/ipc/mojo/public/LICENSE b/utils/ipc/mojo/public/LICENSE
> index 972bb2edb099..513e8a6a0a1d 100644
> --- a/utils/ipc/mojo/public/LICENSE
> +++ b/utils/ipc/mojo/public/LICENSE
> @@ -1,4 +1,4 @@
> -// Copyright 2014 The Chromium Authors. All rights reserved.
> +// Copyright 2014 The Chromium Authors
>  //
>  // Redistribution and use in source and binary forms, with or without
>  // modification, are permitted provided that the following conditions are
> diff --git a/utils/ipc/mojo/public/tools/BUILD.gn b/utils/ipc/mojo/public/tools/BUILD.gn
> index eb6391a65400..5328a34a3935 100644
> --- a/utils/ipc/mojo/public/tools/BUILD.gn
> +++ b/utils/ipc/mojo/public/tools/BUILD.gn
> @@ -1,4 +1,4 @@
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -10,7 +10,11 @@ group("mojo_python_unittests") {
>      "run_all_python_unittests.py",
>      "//testing/scripts/run_isolated_script_test.py",
>    ]
> -  deps = [ "//mojo/public/tools/mojom/mojom:tests" ]
> +  deps = [
> +    "//mojo/public/tools/bindings:tests",
> +    "//mojo/public/tools/mojom:tests",
> +    "//mojo/public/tools/mojom/mojom:tests",
> +  ]
>    data_deps = [
>      "//testing:test_scripts_shared",
>      "//third_party/catapult/third_party/typ/",
> diff --git a/utils/ipc/mojo/public/tools/bindings/BUILD.gn b/utils/ipc/mojo/public/tools/bindings/BUILD.gn
> index 3e2425327490..eeca73ea3d56 100644
> --- a/utils/ipc/mojo/public/tools/bindings/BUILD.gn
> +++ b/utils/ipc/mojo/public/tools/bindings/BUILD.gn
> @@ -1,24 +1,27 @@
> -# Copyright 2016 The Chromium Authors. All rights reserved.
> +# Copyright 2016 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import("//build/config/python.gni")
>  import("//mojo/public/tools/bindings/mojom.gni")
>  import("//third_party/jinja2/jinja2.gni")
>  
> -# TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -python2_action("precompile_templates") {
> +action("precompile_templates") {
>    sources = mojom_generator_sources
>    sources += [
> +    "$mojom_generator_root/generators/cpp_templates/cpp_macros.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/enum_macros.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/enum_serialization_declaration.tmpl",
> +    "$mojom_generator_root/generators/cpp_templates/feature_declaration.tmpl",
> +    "$mojom_generator_root/generators/cpp_templates/feature_definition.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/interface_declaration.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/interface_definition.tmpl",
> +    "$mojom_generator_root/generators/cpp_templates/interface_feature_declaration.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/interface_macros.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/interface_proxy_declaration.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/interface_request_validator_declaration.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/interface_response_validator_declaration.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/interface_stub_declaration.tmpl",
> +    "$mojom_generator_root/generators/cpp_templates/module-features.h.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/module-forward.h.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/module-import-headers.h.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/module-params-data.h.tmpl",
> @@ -26,7 +29,6 @@ python2_action("precompile_templates") {
>      "$mojom_generator_root/generators/cpp_templates/module-shared-message-ids.h.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/module-shared.cc.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/module-shared.h.tmpl",
> -    "$mojom_generator_root/generators/cpp_templates/module-test-utils.cc.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/module-test-utils.h.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/module.cc.tmpl",
>      "$mojom_generator_root/generators/cpp_templates/module.h.tmpl",
> @@ -65,9 +67,6 @@ python2_action("precompile_templates") {
>      "$mojom_generator_root/generators/java_templates/struct.java.tmpl",
>      "$mojom_generator_root/generators/java_templates/union.java.tmpl",
>      "$mojom_generator_root/generators/js_templates/enum_definition.tmpl",
> -    "$mojom_generator_root/generators/js_templates/externs/interface_definition.tmpl",
> -    "$mojom_generator_root/generators/js_templates/externs/module.externs.tmpl",
> -    "$mojom_generator_root/generators/js_templates/externs/struct_definition.tmpl",
>      "$mojom_generator_root/generators/js_templates/fuzzing.tmpl",
>      "$mojom_generator_root/generators/js_templates/interface_definition.tmpl",
>      "$mojom_generator_root/generators/js_templates/lite/enum_definition.tmpl",
> @@ -93,8 +92,11 @@ python2_action("precompile_templates") {
>      "$mojom_generator_root/generators/mojolpm_templates/mojolpm_macros.tmpl",
>      "$mojom_generator_root/generators/mojolpm_templates/mojolpm_to_proto_macros.tmpl",
>      "$mojom_generator_root/generators/mojolpm_templates/mojolpm_traits_specialization_macros.tmpl",
> +    "$mojom_generator_root/generators/ts_templates/enum_definition.tmpl",
> +    "$mojom_generator_root/generators/ts_templates/interface_definition.tmpl",
>      "$mojom_generator_root/generators/ts_templates/module_definition.tmpl",
> -    "$mojom_generator_root/generators/ts_templates/mojom.tmpl",
> +    "$mojom_generator_root/generators/ts_templates/struct_definition.tmpl",
> +    "$mojom_generator_root/generators/ts_templates/union_definition.tmpl",
>    ]
>    script = mojom_generator_script
>  
> @@ -102,8 +104,8 @@ python2_action("precompile_templates") {
>    outputs = [
>      "$target_gen_dir/cpp_templates.zip",
>      "$target_gen_dir/java_templates.zip",
> -    "$target_gen_dir/mojolpm_templates.zip",
>      "$target_gen_dir/js_templates.zip",
> +    "$target_gen_dir/mojolpm_templates.zip",
>      "$target_gen_dir/ts_templates.zip",
>    ]
>    args = [
> @@ -113,3 +115,17 @@ python2_action("precompile_templates") {
>      "precompile",
>    ]
>  }
> +
> +group("tests") {
> +  data = [
> +    mojom_generator_script,
> +    "checks/mojom_attributes_check_unittest.py",
> +    "checks/mojom_interface_feature_check_unittest.py",
> +    "checks/mojom_restrictions_checks_unittest.py",
> +    "mojom_bindings_generator_unittest.py",
> +    "//tools/diagnosis/crbug_1001171.py",
> +    "//third_party/markupsafe/",
> +  ]
> +  data += mojom_generator_sources
> +  data += jinja2_sources
> +}
> diff --git a/utils/ipc/mojo/public/tools/bindings/README.md b/utils/ipc/mojo/public/tools/bindings/README.md
> index 438824502280..b27b2d01b3fc 100644
> --- a/utils/ipc/mojo/public/tools/bindings/README.md
> +++ b/utils/ipc/mojo/public/tools/bindings/README.md
> @@ -96,7 +96,7 @@ for message parameters.
>  | `string`                      | UTF-8 encoded string.
>  | `array<T>`                    | Array of any Mojom type *T*; for example, `array<uint8>` or `array<array<string>>`.
>  | `array<T, N>`                 | Fixed-length array of any Mojom type *T*. The parameter *N* must be an integral constant.
> -| `map<S, T>`                   | Associated array maping values of type *S* to values of type *T*. *S* may be a `string`, `enum`, or numeric type.
> +| `map<S, T>`                   | Associated array mapping values of type *S* to values of type *T*. *S* may be a `string`, `enum`, or numeric type.
>  | `handle`                      | Generic Mojo handle. May be any type of handle, including a wrapped native platform handle.
>  | `handle<message_pipe>`        | Generic message pipe handle.
>  | `handle<shared_buffer>`       | Shared buffer handle.
> @@ -188,8 +188,8 @@ struct StringPair {
>  };
>  
>  enum AnEnum {
> -  YES,
> -  NO
> +  kYes,
> +  kNo
>  };
>  
>  interface SampleInterface {
> @@ -209,7 +209,7 @@ struct AllTheThings {
>    uint64 unsigned_64bit_value;
>    float float_value_32bit;
>    double float_value_64bit;
> -  AnEnum enum_value = AnEnum.YES;
> +  AnEnum enum_value = AnEnum.kYes;
>  
>    // Strings may be nullable.
>    string? maybe_a_string_maybe_not;
> @@ -300,14 +300,14 @@ within a module or nested within the namespace of some struct or interface:
>  module business.mojom;
>  
>  enum Department {
> -  SALES = 0,
> -  DEV,
> +  kSales = 0,
> +  kDev,
>  };
>  
>  struct Employee {
>    enum Type {
> -    FULL_TIME,
> -    PART_TIME,
> +    kFullTime,
> +    kPartTime,
>    };
>  
>    Type type;
> @@ -315,6 +315,9 @@ struct Employee {
>  };
>  ```
>  
> +C++ constant-style enum value names are preferred as specified in the
> +[Google C++ Style Guide](https://google.github.io/styleguide/cppguide.html#Enumerator_Names).
> +
>  Similar to C-style enums, individual values may be explicitly assigned within an
>  enum definition. By default, values are based at zero and increment by
>  1 sequentially.
> @@ -336,8 +339,8 @@ struct Employee {
>    const uint64 kInvalidId = 0;
>  
>    enum Type {
> -    FULL_TIME,
> -    PART_TIME,
> +    kFullTime,
> +    kPartTime,
>    };
>  
>    uint64 id = kInvalidId;
> @@ -348,6 +351,37 @@ struct Employee {
>  The effect of nested definitions on generated bindings varies depending on the
>  target language. See [documentation for individual target languages](#Generated-Code-For-Target-Languages).
>  
> +### Features
> +
> +Features can be declared with a `name` and `default_state` and can be attached
> +in mojo to interfaces or methods using the `RuntimeFeature` attribute. If the
> +feature is disabled at runtime, the method will crash and the interface will
> +refuse to be bound / instantiated. Features cannot be serialized to be sent over
> +IPC at this time.
> +
> +```
> +module experimental.mojom;
> +
> +feature kUseElevators {
> +  const string name = "UseElevators";
> +  const bool default_state = false;
> +}
> +
> +[RuntimeFeature=kUseElevators]
> +interface Elevator {
> +  // This interface cannot be bound or called if the feature is disabled.
> +}
> +
> +interface Building {
> +  // This method cannot be called if the feature is disabled.
> +  [RuntimeFeature=kUseElevators]
> +  CallElevator(int floor);
> +
> +  // This method can be called.
> +  RingDoorbell(int volume);
> +}
> +```
> +
>  ### Interfaces
>  
>  An **interface** is a logical bundle of parameterized request messages. Each
> @@ -396,20 +430,33 @@ interesting attributes supported today.
>    extreme caution, because it can lead to deadlocks otherwise.
>  
>  * **`[Default]`**:
> -  The `Default` attribute may be used to specify an enumerator value that
> -  will be used if an `Extensible` enumeration does not deserialize to a known
> -  value on the receiver side, i.e. the sender is using a newer version of the
> -  enum. This allows unknown values to be mapped to a well-defined value that can
> -  be appropriately handled.
> +  The `Default` attribute may be used to specify an enumerator value or union
> +  field that will be used if an `Extensible` enumeration or union does not
> +  deserialize to a known value on the receiver side, i.e. the sender is using a
> +  newer version of the enum or union. This allows unknown values to be mapped to
> +  a well-defined value that can be appropriately handled.
> +
> +  Note: The `Default` field for a union must be of nullable or integral type.
> +  When a union is defaulted to this field, the field takes on the default value
> +  for its type: null for nullable types, and zero/false for integral types.
>  
>  * **`[Extensible]`**:
> -  The `Extensible` attribute may be specified for any enum definition. This
> -  essentially disables builtin range validation when receiving values of the
> -  enum type in a message, allowing older bindings to tolerate unrecognized
> -  values from newer versions of the enum.
> +  The `Extensible` attribute may be specified for any enum or union definition.
> +  For enums, this essentially disables builtin range validation when receiving
> +  values of the enum type in a message, allowing older bindings to tolerate
> +  unrecognized values from newer versions of the enum.
>  
> -  Note: in the future, an `Extensible` enumeration will require that a `Default`
> -  enumerator value also be specified.
> +  If an enum value within an extensible enum definition is affixed with the
> +  `Default` attribute, out-of-range values for the enum will deserialize to that
> +  default value. Only one enum value may be designated as the `Default`.
> +
> +  Similarly, a union marked `Extensible` will deserialize to its `Default` field
> +  when an unrecognized field is received. Extensible unions MUST specify exactly
> +  one `Default` field, and the field must be of nullable or integral type. When
> +  defaulted to this field, the value is always null/zero/false as appropriate.
> +
> +  An `Extensible` enumeration REQUIRES that a `Default` value be specified,
> +  so all new extensible enums should specify one.
>  
>  * **`[Native]`**:
>    The `Native` attribute may be specified for an empty struct declaration to
> @@ -422,7 +469,10 @@ interesting attributes supported today.
>  * **`[MinVersion=N]`**:
>    The `MinVersion` attribute is used to specify the version at which a given
>    field, enum value, interface method, or method parameter was introduced.
> -  See [Versioning](#Versioning) for more details.
> +  See [Versioning](#Versioning) for more details. `MinVersion` does not apply
> +  to interfaces, structs or enums, but to the fields of those types.
> +  `MinVersion` is not a module-global value, but it is ok to pretend it is by
> +  skipping versions when adding fields or parameters.
>  
>  * **`[Stable]`**:
>    The `Stable` attribute specifies that a given mojom type or interface
> @@ -442,13 +492,73 @@ interesting attributes supported today.
>    string representation as specified by RFC 4122. New UUIDs can be generated
>    with common tools such as `uuidgen`.
>  
> +* **`[RuntimeFeature=feature]`**
> +  The `RuntimeFeature` attribute should reference a mojo `feature`. If this
> +  feature is enabled (e.g. using `--enable-features={feature.name}`) then the
> +  interface behaves entirely as expected. If the feature is not enabled the
> +  interface cannot be bound to a concrete receiver or remote - attempting to do
> +  so will result in the receiver or remote being reset() to an unbound state.
> +  Note that this is a different concept to the build-time `EnableIf` directive.
> +  `RuntimeFeature` is currently only supported for C++ bindings and has no
> +  effect for, say, Java or TypeScript bindings (see https://crbug.com/1278253).
> +
>  * **`[EnableIf=value]`**:
>    The `EnableIf` attribute is used to conditionally enable definitions when the
>    mojom is parsed. If the `mojom` target in the GN file does not include the
>    matching `value` in the list of `enabled_features`, the definition will be
>    disabled. This is useful for mojom definitions that only make sense on one
>    platform. Note that the `EnableIf` attribute can only be set once per
> -  definition.
> +  definition and cannot be set at the same time as `EnableIfNot`. Also be aware
> +  that only one condition can be tested, `EnableIf=value,xyz` introduces a new
> +  `xyz` attribute. `xyz` is not part of the `EnableIf` condition that depends
> +  only on the feature `value`. Complex conditions can be introduced via
> +  enabled_features in `build.gn` files.
> +
> +* **`[EnableIfNot=value]`**:
> +  The `EnableIfNot` attribute is used to conditionally enable definitions when
> +  the mojom is parsed. If the `mojom` target in the GN file includes the
> +  matching `value` in the list of `enabled_features`, the definition will be
> +  disabled. This is useful for mojom definitions that only make sense on all but
> +  one platform. Note that the `EnableIfNot` attribute can only be set once per
> +  definition and cannot be set at the same time as `EnableIf`.
> +
> +* **`[ServiceSandbox=value]`**:
> +  The `ServiceSandbox` attribute is used in Chromium to tag which sandbox a
> +  service hosting an implementation of interface will be launched in. This only
> +  applies to `C++` bindings. `value` should match a constant defined in an
> +  imported `sandbox.mojom.Sandbox` enum (for Chromium this is
> +  `//sandbox/policy/mojom/sandbox.mojom`), such as `kService`.
> +
> +* **`[RequireContext=enum]`**:
> +  The `RequireContext` attribute is used in Chromium to tag interfaces that
> +  should be passed (as remotes or receivers) only to privileged process
> +  contexts. The process context must be an enum that is imported into the
> +  mojom that defines the tagged interface. `RequireContext` may be used in
> +  future to DCHECK or CHECK if remotes are made available in contexts that
> +  conflict with the one provided in the interface definition. Process contexts
> +  are not the same as the sandbox a process is running in, but will reflect
> +  the set of capabilities provided to the service.
> +
> +* **`[AllowedContext=enum]`**:
> +  The `AllowedContext` attribute is used in Chromium to tag methods that pass
> +  remotes or receivers of interfaces that are marked with a `RequireContext`
> +  attribute. The enum provided on the method must be equal or better (lower
> +  numerically) than the one required on the interface being passed. At present
> +  failing to specify an adequate `AllowedContext` value will cause mojom
> +  generation to fail at compile time. In future DCHECKs or CHECKs might be
> +  added to enforce that method is only called from a process context that meets
> +  the given `AllowedContext` value. The enum must of the same type as that
> +  specified in the interface's `RequireContext` attribute. Adding an
> +  `AllowedContext` attribute to a method is a strong indication that you need
> +   a detailed security review of your design - please reach out to the security
> +   team.
> +
> +* **`[SupportsUrgent]`**:
> +  The `SupportsUrgent` attribute is used in conjunction with
> +  `mojo::UrgentMessageScope` in Chromium to tag messages as having high
> +  priority. The IPC layer notifies the underlying scheduler upon both receiving
> +  and processing an urgent message. At present, this attribute only affects
> +  channel associated messages in the renderer process.
>  
>  ## Generated Code For Target Languages
>  
> @@ -495,9 +605,9 @@ values. For example if a Mojom declares the enum:
>  
>  ``` cpp
>  enum AdvancedBoolean {
> -  TRUE = 0,
> -  FALSE = 1,
> -  FILE_NOT_FOUND = 2,
> +  kTrue = 0,
> +  kFalse = 1,
> +  kFileNotFound = 2,
>  };
>  ```
>  
> @@ -550,10 +660,16 @@ See the documentation for
>  
>  *** note
>  **NOTE:** You don't need to worry about versioning if you don't care about
> -backwards compatibility. Specifically, all parts of Chrome are updated
> -atomically today and there is not yet any possibility of any two Chrome
> -processes communicating with two different versions of any given Mojom
> -interface.
> +backwards compatibility. Today, all parts of the Chrome browser are
> +updated atomically and there is not yet any possibility of any two
> +Chrome processes communicating with two different versions of any given Mojom
> +interface. On Chrome OS, there are several places where versioning is required.
> +For example,
> +[ARC++](https://developer.android.com/chrome-os/intro)
> +uses versioned mojo to send IPC to the Android container.
> +Likewise, the
> +[Lacros](/docs/lacros.md)
> +browser uses versioned mojo to talk to the ash system UI.
>  ***
>  
>  Services extend their interfaces to support new features over time, and clients
> @@ -593,8 +709,8 @@ struct Employee {
>  
>  *** note
>  **NOTE:** Mojo object or handle types added with a `MinVersion` **MUST** be
> -optional (nullable). See [Primitive Types](#Primitive-Types) for details on
> -nullable values.
> +optional (nullable) or primitive. See [Primitive Types](#Primitive-Types) for
> +details on nullable values.
>  ***
>  
>  By default, fields belong to version 0. New fields must be appended to the
> @@ -624,10 +740,10 @@ the following hard constraints:
>  * For any given struct or interface, if any field or method explicitly specifies
>      an ordinal value, all fields or methods must explicitly specify an ordinal
>      value.
> -* For an *N*-field struct or *N*-method interface, the set of explicitly
> -    assigned ordinal values must be limited to the range *[0, N-1]*. Interfaces
> -    should include placeholder methods to fill the ordinal positions of removed
> -    methods (for example "Unused_Message_7 at 7()" or "RemovedMessage at 42()", etc).
> +* For an *N*-field struct, the set of explicitly assigned ordinal values must be
> +    limited to the range *[0, N-1]*. Structs should include placeholder fields
> +    to fill the ordinal positions of removed fields (for example "Unused_Field"
> +    or "RemovedField", etc).
>  
>  You may reorder fields, but you must ensure that the ordinal values of existing
>  fields remain unchanged. For example, the following struct remains
> @@ -652,6 +768,24 @@ There are two dimensions on which an interface can be extended
>      that the version number is scoped to the whole interface rather than to any
>      individual parameter list.
>  
> +``` cpp
> +// Old version:
> +interface HumanResourceDatabase {
> +  QueryEmployee(uint64 id) => (Employee? employee);
> +};
> +
> +// New version:
> +interface HumanResourceDatabase {
> +  QueryEmployee(uint64 id, [MinVersion=1] bool retrieve_finger_print)
> +      => (Employee? employee,
> +          [MinVersion=1] array<uint8>? finger_print);
> +};
> +```
> +
> +Similar to [versioned structs](#Versioned-Structs), when you pass the parameter
> +list of a request or response method to a destination using an older version of
> +an interface, unrecognized fields are silently discarded.
> +
>      Please note that adding a response to a message which did not previously
>      expect a response is a not a backwards-compatible change.
>  
> @@ -664,17 +798,12 @@ For example:
>  ``` cpp
>  // Old version:
>  interface HumanResourceDatabase {
> -  AddEmployee(Employee employee) => (bool success);
>    QueryEmployee(uint64 id) => (Employee? employee);
>  };
>  
>  // New version:
>  interface HumanResourceDatabase {
> -  AddEmployee(Employee employee) => (bool success);
> -
> -  QueryEmployee(uint64 id, [MinVersion=1] bool retrieve_finger_print)
> -      => (Employee? employee,
> -          [MinVersion=1] array<uint8>? finger_print);
> +  QueryEmployee(uint64 id) => (Employee? employee);
>  
>    [MinVersion=1]
>    AttachFingerPrint(uint64 id, array<uint8> finger_print)
> @@ -682,10 +811,7 @@ interface HumanResourceDatabase {
>  };
>  ```
>  
> -Similar to [versioned structs](#Versioned-Structs), when you pass the parameter
> -list of a request or response method to a destination using an older version of
> -an interface, unrecognized fields are silently discarded. However, if the method
> -call itself is not recognized, it is considered a validation error and the
> +If a method call is not recognized, it is considered a validation error and the
>  receiver will close its end of the interface pipe. For example, if a client on
>  version 1 of the above interface sends an `AttachFingerPrint` request to an
>  implementation of version 0, the client will be disconnected.
> @@ -712,8 +838,8 @@ If you want an enum to be extensible in the future, you can apply the
>  ``` cpp
>  [Extensible]
>  enum Department {
> -  SALES,
> -  DEV,
> +  kSales,
> +  kDev,
>  };
>  ```
>  
> @@ -722,9 +848,9 @@ And later you can extend this enum without breaking backwards compatibility:
>  ``` cpp
>  [Extensible]
>  enum Department {
> -  SALES,
> -  DEV,
> -  [MinVersion=1] RESEARCH,
> +  kSales,
> +  kDev,
> +  [MinVersion=1] kResearch,
>  };
>  ```
>  
> @@ -782,7 +908,7 @@ Statement = ModuleStatement | ImportStatement | Definition
>  
>  ModuleStatement = AttributeSection "module" Identifier ";"
>  ImportStatement = "import" StringLiteral ";"
> -Definition = Struct Union Interface Enum Const
> +Definition = Struct Union Interface Enum Feature Const
>  
>  AttributeSection = <empty> | "[" AttributeList "]"
>  AttributeList = <empty> | NonEmptyAttributeList
> @@ -809,7 +935,7 @@ InterfaceBody = <empty>
>                | InterfaceBody Const
>                | InterfaceBody Enum
>                | InterfaceBody Method
> -Method = AttributeSection Name Ordinal "(" ParamterList ")" Response ";"
> +Method = AttributeSection Name Ordinal "(" ParameterList ")" Response ";"
>  ParameterList = <empty> | NonEmptyParameterList
>  NonEmptyParameterList = Parameter
>                        | Parameter "," NonEmptyParameterList
> @@ -847,6 +973,13 @@ EnumValue = AttributeSection Name
>            | AttributeSection Name "=" Integer
>            | AttributeSection Name "=" Identifier
>  
> +; Note: `feature` is a weak keyword and can appear as, say, a struct field name.
> +Feature = AttributeSection "feature" Name "{" FeatureBody "}" ";"
> +       | AttributeSection "feature" Name ";"
> +FeatureBody = <empty>
> +           | FeatureBody FeatureField
> +FeatureField = AttributeSection TypeSpec Name Default ";"
> +
>  Const = "const" TypeSpec Name "=" Constant ";"
>  
>  Constant = Literal | Identifier ";"
> diff --git a/utils/ipc/mojo/public/tools/bindings/checks/__init__.py b/utils/ipc/mojo/public/tools/bindings/checks/__init__.py
> new file mode 100644
> index 000000000000..e69de29bb2d1
> diff --git a/utils/ipc/mojo/public/tools/bindings/checks/mojom_attributes_check.py b/utils/ipc/mojo/public/tools/bindings/checks/mojom_attributes_check.py
> new file mode 100644
> index 000000000000..e6e4f2c9392b
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/bindings/checks/mojom_attributes_check.py
> @@ -0,0 +1,170 @@
> +# Copyright 2022 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +"""Validate mojo attributes are allowed in Chrome before generation."""
> +
> +import mojom.generate.check as check
> +import mojom.generate.module as module
> +
> +_COMMON_ATTRIBUTES = {
> +    'EnableIf',
> +    'EnableIfNot',
> +}
> +
> +# For struct, union & parameter lists.
> +_COMMON_FIELD_ATTRIBUTES = _COMMON_ATTRIBUTES | {
> +    'MinVersion',
> +    'RenamedFrom',
> +}
> +
> +# Note: `Default`` goes on the default _value_, not on the enum.
> +# Note: [Stable] without [Extensible] is not allowed.
> +_ENUM_ATTRIBUTES = _COMMON_ATTRIBUTES | {
> +    'Extensible',
> +    'Native',
> +    'Stable',
> +    'RenamedFrom',
> +    'Uuid',
> +}
> +
> +# TODO(crbug.com/1234883) MinVersion is not needed for EnumVal.
> +_ENUMVAL_ATTRIBUTES = _COMMON_ATTRIBUTES | {
> +    'Default',
> +    'MinVersion',
> +}
> +
> +_INTERFACE_ATTRIBUTES = _COMMON_ATTRIBUTES | {
> +    'RenamedFrom',
> +    'RequireContext',
> +    'RuntimeFeature',
> +    'ServiceSandbox',
> +    'Stable',
> +    'Uuid',
> +}
> +
> +_METHOD_ATTRIBUTES = _COMMON_ATTRIBUTES | {
> +    'AllowedContext',
> +    'MinVersion',
> +    'NoInterrupt',
> +    'RuntimeFeature',
> +    'SupportsUrgent',
> +    'Sync',
> +    'UnlimitedSize',
> +}
> +
> +_MODULE_ATTRIBUTES = _COMMON_ATTRIBUTES | {
> +    'JavaConstantsClassName',
> +    'JavaPackage',
> +}
> +
> +_PARAMETER_ATTRIBUTES = _COMMON_FIELD_ATTRIBUTES
> +
> +_STRUCT_ATTRIBUTES = _COMMON_ATTRIBUTES | {
> +    'CustomSerializer',
> +    'JavaClassName',
> +    'Native',
> +    'Stable',
> +    'RenamedFrom',
> +    'Uuid',
> +}
> +
> +_STRUCT_FIELD_ATTRIBUTES = _COMMON_FIELD_ATTRIBUTES
> +
> +_UNION_ATTRIBUTES = _COMMON_ATTRIBUTES | {
> +    'Extensible',
> +    'Stable',
> +    'RenamedFrom',
> +    'Uuid',
> +}
> +
> +_UNION_FIELD_ATTRIBUTES = _COMMON_FIELD_ATTRIBUTES | {
> +    'Default',
> +}
> +
> +# TODO(https://crbug.com/1193875) empty this set and remove the allowlist.
> +_STABLE_ONLY_ALLOWLISTED_ENUMS = {
> +    'crosapi.mojom.OptionalBool',
> +    'crosapi.mojom.TriState',
> +}
> +
> +
> +class Check(check.Check):
> +  def __init__(self, *args, **kwargs):
> +    super(Check, self).__init__(*args, **kwargs)
> +
> +  def _Respell(self, allowed, attribute):
> +    for a in allowed:
> +      if a.lower() == attribute.lower():
> +        return f" - Did you mean: {a}?"
> +    return ""
> +
> +  def _CheckAttributes(self, context, allowed, attributes):
> +    if not attributes:
> +      return
> +    for attribute in attributes:
> +      if not attribute in allowed:
> +        # Is there a close misspelling?
> +        hint = self._Respell(allowed, attribute)
> +        raise check.CheckException(
> +            self.module,
> +            f"attribute {attribute} not allowed on {context}{hint}")
> +
> +  def _CheckEnumAttributes(self, enum):
> +    if enum.attributes:
> +      self._CheckAttributes("enum", _ENUM_ATTRIBUTES, enum.attributes)
> +      if 'Stable' in enum.attributes and not 'Extensible' in enum.attributes:
> +        full_name = f"{self.module.mojom_namespace}.{enum.mojom_name}"
> +        if full_name not in _STABLE_ONLY_ALLOWLISTED_ENUMS:
> +          raise check.CheckException(
> +              self.module,
> +              f"[Extensible] required on [Stable] enum {full_name}")
> +    for enumval in enum.fields:
> +      self._CheckAttributes("enum value", _ENUMVAL_ATTRIBUTES,
> +                            enumval.attributes)
> +
> +  def _CheckInterfaceAttributes(self, interface):
> +    self._CheckAttributes("interface", _INTERFACE_ATTRIBUTES,
> +                          interface.attributes)
> +    for method in interface.methods:
> +      self._CheckAttributes("method", _METHOD_ATTRIBUTES, method.attributes)
> +      for param in method.parameters:
> +        self._CheckAttributes("parameter", _PARAMETER_ATTRIBUTES,
> +                              param.attributes)
> +      if method.response_parameters:
> +        for param in method.response_parameters:
> +          self._CheckAttributes("parameter", _PARAMETER_ATTRIBUTES,
> +                                param.attributes)
> +    for enum in interface.enums:
> +      self._CheckEnumAttributes(enum)
> +
> +  def _CheckModuleAttributes(self):
> +    self._CheckAttributes("module", _MODULE_ATTRIBUTES, self.module.attributes)
> +
> +  def _CheckStructAttributes(self, struct):
> +    self._CheckAttributes("struct", _STRUCT_ATTRIBUTES, struct.attributes)
> +    for field in struct.fields:
> +      self._CheckAttributes("struct field", _STRUCT_FIELD_ATTRIBUTES,
> +                            field.attributes)
> +    for enum in struct.enums:
> +      self._CheckEnumAttributes(enum)
> +
> +  def _CheckUnionAttributes(self, union):
> +    self._CheckAttributes("union", _UNION_ATTRIBUTES, union.attributes)
> +    for field in union.fields:
> +      self._CheckAttributes("union field", _UNION_FIELD_ATTRIBUTES,
> +                            field.attributes)
> +
> +  def CheckModule(self):
> +    """Note that duplicate attributes are forbidden at the parse phase.
> +    We also do not need to look at the types of any parameters, as they will be
> +    checked where they are defined. Consts do not have attributes so can be
> +    skipped."""
> +    self._CheckModuleAttributes()
> +    for interface in self.module.interfaces:
> +      self._CheckInterfaceAttributes(interface)
> +    for enum in self.module.enums:
> +      self._CheckEnumAttributes(enum)
> +    for struct in self.module.structs:
> +      self._CheckStructAttributes(struct)
> +    for union in self.module.unions:
> +      self._CheckUnionAttributes(union)
> diff --git a/utils/ipc/mojo/public/tools/bindings/checks/mojom_attributes_check_unittest.py b/utils/ipc/mojo/public/tools/bindings/checks/mojom_attributes_check_unittest.py
> new file mode 100644
> index 000000000000..f1a50a4ab508
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/bindings/checks/mojom_attributes_check_unittest.py
> @@ -0,0 +1,194 @@
> +# Copyright 2022 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +
> +import unittest
> +
> +import mojom.generate.check as check
> +from mojom_bindings_generator import LoadChecks, _Generate
> +from mojom_parser_test_case import MojomParserTestCase
> +
> +
> +class FakeArgs:
> +  """Fakes args to _Generate - intention is to do just enough to run checks"""
> +
> +  def __init__(self, tester, files=None):
> +    """ `tester` is MojomParserTestCase for paths.
> +        `files` will have tester path added."""
> +    self.checks_string = 'attributes'
> +    self.depth = tester.GetPath('')
> +    self.filelist = None
> +    self.filename = [tester.GetPath(x) for x in files]
> +    self.gen_directories = tester.GetPath('gen')
> +    self.generators_string = ''
> +    self.import_directories = []
> +    self.output_dir = tester.GetPath('out')
> +    self.scrambled_message_id_salt_paths = None
> +    self.typemaps = []
> +    self.variant = 'none'
> +
> +
> +class MojoBindingsCheckTest(MojomParserTestCase):
> +  def _ParseAndGenerate(self, mojoms):
> +    self.ParseMojoms(mojoms)
> +    args = FakeArgs(self, files=mojoms)
> +    _Generate(args, {})
> +
> +  def _testValid(self, filename, content):
> +    self.WriteFile(filename, content)
> +    self._ParseAndGenerate([filename])
> +
> +  def _testThrows(self, filename, content, regexp):
> +    mojoms = []
> +    self.WriteFile(filename, content)
> +    mojoms.append(filename)
> +    with self.assertRaisesRegexp(check.CheckException, regexp):
> +      self._ParseAndGenerate(mojoms)
> +
> +  def testLoads(self):
> +    """Validate that the check is registered under the expected name."""
> +    check_modules = LoadChecks('attributes')
> +    self.assertTrue(check_modules['attributes'])
> +
> +  def testNoAnnotations(self):
> +    # Undecorated mojom should be fine.
> +    self._testValid(
> +        "a.mojom", """
> +      module a;
> +      struct Bar { int32 a; };
> +      enum Hello { kValue };
> +      union Thingy { Bar b; Hello hi; };
> +      interface Foo {
> +        Foo(int32 a, Hello hi, Thingy t) => (Bar b);
> +      };
> +    """)
> +
> +  def testValidAnnotations(self):
> +    # Obviously this is meaningless and won't generate, but it should pass
> +    # the attribute check's validation.
> +    self._testValid(
> +        "a.mojom", """
> +      [JavaConstantsClassName="FakeClass",JavaPackage="org.chromium.Fake"]
> +      module a;
> +      [Stable, Extensible]
> +      enum Hello { [Default] kValue, kValue2, [MinVersion=2] kValue3 };
> +      [Native]
> +      enum NativeEnum {};
> +      [Stable,Extensible]
> +      union Thingy { Bar b; [Default]int32 c; Hello hi; };
> +
> +      [Stable,RenamedFrom="module.other.Foo",
> +       Uuid="4C178401-4B07-4C2E-9255-5401A943D0C7"]
> +      struct Structure { Hello hi; };
> +
> +      [ServiceSandbox=Hello.kValue,RequireContext=Hello.kValue,Stable,
> +       Uuid="2F17D7DD-865A-4B1C-9394-9C94E035E82F"]
> +      interface Foo {
> +        [AllowedContext=Hello.kValue]
> +        Foo at 0(int32 a) => (int32 b);
> +        [MinVersion=2,Sync,UnlimitedSize,NoInterrupt]
> +        Bar at 1(int32 b, [MinVersion=2]Structure? s) => (bool c);
> +      };
> +
> +      [RuntimeFeature=test.mojom.FeatureName]
> +      interface FooFeatureControlled {};
> +
> +      interface FooMethodFeatureControlled {
> +        [RuntimeFeature=test.mojom.FeatureName]
> +        MethodWithFeature() => (bool c);
> +      };
> +    """)
> +
> +  def testWrongModuleStable(self):
> +    contents = """
> +      // err: module cannot be Stable
> +      [Stable]
> +      module a;
> +      enum Hello { kValue, kValue2, kValue3 };
> +      enum NativeEnum {};
> +      struct Structure { Hello hi; };
> +
> +      interface Foo {
> +        Foo(int32 a) => (int32 b);
> +        Bar(int32 b, Structure? s) => (bool c);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents,
> +                     'attribute Stable not allowed on module')
> +
> +  def testWrongEnumDefault(self):
> +    contents = """
> +      module a;
> +      // err: default should go on EnumValue not Enum.
> +      [Default=kValue]
> +      enum Hello { kValue, kValue2, kValue3 };
> +      enum NativeEnum {};
> +      struct Structure { Hello hi; };
> +
> +      interface Foo {
> +        Foo(int32 a) => (int32 b);
> +        Bar(int32 b, Structure? s) => (bool c);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents,
> +                     'attribute Default not allowed on enum')
> +
> +  def testWrongStructMinVersion(self):
> +    contents = """
> +      module a;
> +      enum Hello { kValue, kValue2, kValue3 };
> +      enum NativeEnum {};
> +      // err: struct cannot have MinVersion.
> +      [MinVersion=2]
> +      struct Structure { Hello hi; };
> +
> +      interface Foo {
> +        Foo(int32 a) => (int32 b);
> +        Bar(int32 b, Structure? s) => (bool c);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents,
> +                     'attribute MinVersion not allowed on struct')
> +
> +  def testWrongMethodRequireContext(self):
> +    contents = """
> +      module a;
> +      enum Hello { kValue, kValue2, kValue3 };
> +      enum NativeEnum {};
> +      struct Structure { Hello hi; };
> +
> +      interface Foo {
> +        // err: RequireContext is for interfaces.
> +        [RequireContext=Hello.kValue]
> +        Foo(int32 a) => (int32 b);
> +        Bar(int32 b, Structure? s) => (bool c);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents,
> +                     'RequireContext not allowed on method')
> +
> +  def testWrongMethodRequireContext(self):
> +    # crbug.com/1230122
> +    contents = """
> +      module a;
> +      interface Foo {
> +        // err: sync not Sync.
> +        [sync]
> +        Foo(int32 a) => (int32 b);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents,
> +                     'attribute sync not allowed.*Did you mean: Sync')
> +
> +  def testStableExtensibleEnum(self):
> +    # crbug.com/1193875
> +    contents = """
> +      module a;
> +      [Stable]
> +      enum Foo {
> +        kDefaultVal,
> +        kOtherVal = 2,
> +      };
> +    """
> +    self._testThrows('a.mojom', contents,
> +                     'Extensible.*?required.*?Stable.*?enum')
> diff --git a/utils/ipc/mojo/public/tools/bindings/checks/mojom_definitions_check.py b/utils/ipc/mojo/public/tools/bindings/checks/mojom_definitions_check.py
> new file mode 100644
> index 000000000000..702d41c30fc1
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/bindings/checks/mojom_definitions_check.py
> @@ -0,0 +1,34 @@
> +# Copyright 2022 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +"""Ensure no duplicate type definitions before generation."""
> +
> +import mojom.generate.check as check
> +import mojom.generate.module as module
> +
> +
> +class Check(check.Check):
> +  def __init__(self, *args, **kwargs):
> +    super(Check, self).__init__(*args, **kwargs)
> +
> +  def CheckModule(self):
> +    kinds = dict()
> +    for module in self.module.imports:
> +      for kind in module.enums + module.structs + module.unions:
> +        kind_name = f'{kind.module.mojom_namespace}.{kind.mojom_name}'
> +        if kind_name in kinds:
> +          previous_module = kinds[kind_name]
> +          if previous_module.path != module.path:
> +            raise check.CheckException(
> +                self.module, f"multiple-definition for type {kind_name}" +
> +                f"(defined in both {previous_module} and {module})")
> +        kinds[kind_name] = kind.module
> +
> +    for kind in self.module.enums + self.module.structs + self.module.unions:
> +      kind_name = f'{kind.module.mojom_namespace}.{kind.mojom_name}'
> +      if kind_name in kinds:
> +        previous_module = kinds[kind_name]
> +        raise check.CheckException(
> +            self.module, f"multiple-definition for type {kind_name}" +
> +            f"(previous definition in {previous_module})")
> +    return True
> diff --git a/utils/ipc/mojo/public/tools/bindings/checks/mojom_interface_feature_check.py b/utils/ipc/mojo/public/tools/bindings/checks/mojom_interface_feature_check.py
> new file mode 100644
> index 000000000000..07f51a64feaf
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/bindings/checks/mojom_interface_feature_check.py
> @@ -0,0 +1,62 @@
> +# Copyright 2023 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +"""Validate mojo runtime feature guarded interfaces are nullable."""
> +
> +import mojom.generate.check as check
> +import mojom.generate.module as module
> +
> +
> +class Check(check.Check):
> +  def __init__(self, *args, **kwargs):
> +    super(Check, self).__init__(*args, **kwargs)
> +
> +  # `param` is an Interface of some sort.
> +  def _CheckNonNullableFeatureGuardedInterface(self, kind):
> +    # Only need to validate interface if it has a RuntimeFeature
> +    if not kind.kind.runtime_feature:
> +      return
> +    # Nullable (optional) is ok as the interface expects they might not be sent.
> +    if kind.is_nullable:
> +      return
> +    interface = kind.kind.mojom_name
> +    raise check.CheckException(
> +        self.module,
> +        f"interface {interface} has a RuntimeFeature but is not nullable")
> +
> +  # `param` can be a lot of things so check if it is a remote/receiver.
> +  # Array/Map must be recursed into.
> +  def _CheckFieldOrParam(self, kind):
> +    if module.IsAnyInterfaceKind(kind):
> +      self._CheckNonNullableFeatureGuardedInterface(kind)
> +    if module.IsArrayKind(kind):
> +      self._CheckFieldOrParam(kind.kind)
> +    if module.IsMapKind(kind):
> +      self._CheckFieldOrParam(kind.key_kind)
> +      self._CheckFieldOrParam(kind.value_kind)
> +
> +  def _CheckInterfaceFeatures(self, interface):
> +    for method in interface.methods:
> +      for param in method.parameters:
> +        self._CheckFieldOrParam(param.kind)
> +      if method.response_parameters:
> +        for param in method.response_parameters:
> +          self._CheckFieldOrParam(param.kind)
> +
> +  def _CheckStructFeatures(self, struct):
> +    for field in struct.fields:
> +      self._CheckFieldOrParam(field.kind)
> +
> +  def _CheckUnionFeatures(self, union):
> +    for field in union.fields:
> +      self._CheckFieldOrParam(field.kind)
> +
> +  def CheckModule(self):
> +    """Validate that any runtime feature guarded interfaces that might be passed
> +    over mojo are nullable."""
> +    for interface in self.module.interfaces:
> +      self._CheckInterfaceFeatures(interface)
> +    for struct in self.module.structs:
> +      self._CheckStructFeatures(struct)
> +    for union in self.module.unions:
> +      self._CheckUnionFeatures(union)
> diff --git a/utils/ipc/mojo/public/tools/bindings/checks/mojom_interface_feature_check_unittest.py b/utils/ipc/mojo/public/tools/bindings/checks/mojom_interface_feature_check_unittest.py
> new file mode 100644
> index 000000000000..e96152fdd0ef
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/bindings/checks/mojom_interface_feature_check_unittest.py
> @@ -0,0 +1,173 @@
> +# Copyright 2023 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +
> +import unittest
> +
> +import mojom.generate.check as check
> +from mojom_bindings_generator import LoadChecks, _Generate
> +from mojom_parser_test_case import MojomParserTestCase
> +
> +
> +class FakeArgs:
> +  """Fakes args to _Generate - intention is to do just enough to run checks"""
> +  def __init__(self, tester, files=None):
> +    """ `tester` is MojomParserTestCase for paths.
> +        `files` will have tester path added."""
> +    self.checks_string = 'features'
> +    self.depth = tester.GetPath('')
> +    self.filelist = None
> +    self.filename = [tester.GetPath(x) for x in files]
> +    self.gen_directories = tester.GetPath('gen')
> +    self.generators_string = ''
> +    self.import_directories = []
> +    self.output_dir = tester.GetPath('out')
> +    self.scrambled_message_id_salt_paths = None
> +    self.typemaps = []
> +    self.variant = 'none'
> +
> +
> +class MojoBindingsCheckTest(MojomParserTestCase):
> +  def _ParseAndGenerate(self, mojoms):
> +    self.ParseMojoms(mojoms)
> +    args = FakeArgs(self, files=mojoms)
> +    _Generate(args, {})
> +
> +  def assertValid(self, filename, content):
> +    self.WriteFile(filename, content)
> +    self._ParseAndGenerate([filename])
> +
> +  def assertThrows(self, filename, content, regexp):
> +    mojoms = []
> +    self.WriteFile(filename, content)
> +    mojoms.append(filename)
> +    with self.assertRaisesRegexp(check.CheckException, regexp):
> +      self._ParseAndGenerate(mojoms)
> +
> +  def testLoads(self):
> +    """Validate that the check is registered under the expected name."""
> +    check_modules = LoadChecks('features')
> +    self.assertTrue(check_modules['features'])
> +
> +  def testNullableOk(self):
> +    self.assertValid(
> +        "a.mojom", """
> +          module a;
> +          // Scaffolding.
> +          feature kFeature {
> +            const string name = "Hello";
> +            const bool enabled_state = false;
> +          };
> +          [RuntimeFeature=kFeature]
> +          interface Guarded {
> +          };
> +
> +          // Unguarded interfaces should be ok everywhere.
> +          interface NotGuarded { };
> +
> +          // Optional (nullable) interfaces should be ok everywhere:
> +          struct Bar {
> +            pending_remote<Guarded>? remote;
> +            pending_receiver<Guarded>? receiver;
> +          };
> +          union Thingy {
> +            pending_remote<Guarded>? remote;
> +            pending_receiver<Guarded>? receiver;
> +          };
> +          interface Foo {
> +            Foo(
> +              pending_remote<Guarded>? remote,
> +              pending_receiver<Guarded>? receiver,
> +              pending_associated_remote<Guarded>? a_remote,
> +              pending_associated_receiver<Guarded>? a_receiver,
> +              // Unguarded interfaces do not have to be nullable.
> +              pending_remote<NotGuarded> remote,
> +              pending_receiver<NotGuarded> receiver,
> +              pending_associated_remote<NotGuarded> a_remote,
> +              pending_associated_receiver<NotGuarded> a_receiver
> +            ) => (
> +              pending_remote<Guarded>? remote,
> +              pending_receiver<Guarded>? receiver
> +            );
> +            Bar(array<pending_remote<Guarded>?> remote)
> +              => (map<string, pending_receiver<Guarded>?> a);
> +          };
> +    """)
> +
> +  def testMethodParamsMustBeNullable(self):
> +    prelude = """
> +      module a;
> +      // Scaffolding.
> +      feature kFeature {
> +        const string name = "Hello";
> +        const bool enabled_state = false;
> +      };
> +      [RuntimeFeature=kFeature]
> +      interface Guarded { };
> +    """
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          interface Trial {
> +            Method(pending_remote<Guarded> a) => ();
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          interface Trial {
> +            Method(bool foo) => (pending_receiver<Guarded> a);
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          interface Trial {
> +            Method(pending_receiver<Guarded> a) => ();
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          interface Trial {
> +            Method(pending_associated_remote<Guarded> a) => ();
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          interface Trial {
> +            Method(pending_associated_receiver<Guarded> a) => ();
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          interface Trial {
> +            Method(array<pending_associated_receiver<Guarded>> a) => ();
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          interface Trial {
> +            Method(map<string, pending_associated_receiver<Guarded>> a) => ();
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> +
> +  def testStructUnionMembersMustBeNullable(self):
> +    prelude = """
> +      module a;
> +      // Scaffolding.
> +      feature kFeature {
> +        const string name = "Hello";
> +        const bool enabled_state = false;
> +      };
> +      [RuntimeFeature=kFeature]
> +      interface Guarded { };
> +    """
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          struct Trial {
> +            pending_remote<Guarded> a;
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> +    self.assertThrows(
> +        'a.mojom', prelude + """
> +          union Trial {
> +            pending_remote<Guarded> a;
> +          };
> +                     """, 'interface Guarded has a RuntimeFeature')
> diff --git a/utils/ipc/mojo/public/tools/bindings/checks/mojom_restrictions_check.py b/utils/ipc/mojo/public/tools/bindings/checks/mojom_restrictions_check.py
> new file mode 100644
> index 000000000000..d570e26cea68
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/bindings/checks/mojom_restrictions_check.py
> @@ -0,0 +1,102 @@
> +# Copyright 2022 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +"""Validate RequireContext and AllowedContext annotations before generation."""
> +
> +import mojom.generate.check as check
> +import mojom.generate.module as module
> +
> +
> +class Check(check.Check):
> +  def __init__(self, *args, **kwargs):
> +    self.kind_to_interfaces = dict()
> +    super(Check, self).__init__(*args, **kwargs)
> +
> +  def _IsPassedInterface(self, candidate):
> +    if isinstance(
> +        candidate.kind,
> +        (module.PendingReceiver, module.PendingRemote,
> +         module.PendingAssociatedReceiver, module.PendingAssociatedRemote)):
> +      return True
> +    return False
> +
> +  def _CheckInterface(self, method, param):
> +    # |param| is a pending_x<Interface> so need .kind.kind to get Interface.
> +    interface = param.kind.kind
> +    if interface.require_context:
> +      if method.allowed_context is None:
> +        raise check.CheckException(
> +            self.module, "method `{}` has parameter `{}` which passes interface"
> +            " `{}` that requires an AllowedContext annotation but none exists.".
> +            format(
> +                method.mojom_name,
> +                param.mojom_name,
> +                interface.mojom_name,
> +            ))
> +      # If a string was provided, or if an enum was not imported, this will
> +      # be a string and we cannot validate that it is in range.
> +      if not isinstance(method.allowed_context, module.EnumValue):
> +        raise check.CheckException(
> +            self.module,
> +            "method `{}` has AllowedContext={} which is not a valid enum value."
> +            .format(method.mojom_name, method.allowed_context))
> +      # EnumValue must be from the same enum to be compared.
> +      if interface.require_context.enum != method.allowed_context.enum:
> +        raise check.CheckException(
> +            self.module, "method `{}` has parameter `{}` which passes interface"
> +            " `{}` that requires AllowedContext={} but one of kind `{}` was "
> +            "provided.".format(
> +                method.mojom_name,
> +                param.mojom_name,
> +                interface.mojom_name,
> +                interface.require_context.enum,
> +                method.allowed_context.enum,
> +            ))
> +      # RestrictContext enums have most privileged field first (lowest value).
> +      interface_value = interface.require_context.field.numeric_value
> +      method_value = method.allowed_context.field.numeric_value
> +      if interface_value < method_value:
> +        raise check.CheckException(
> +            self.module, "RequireContext={} > AllowedContext={} for method "
> +            "`{}` which passes interface `{}`.".format(
> +                interface.require_context.GetSpec(),
> +                method.allowed_context.GetSpec(), method.mojom_name,
> +                interface.mojom_name))
> +      return True
> +
> +  def _GatherReferencedInterfaces(self, field):
> +    key = field.kind.spec
> +    # structs/unions can nest themselves so we need to bookkeep.
> +    if not key in self.kind_to_interfaces:
> +      # Might reference ourselves so have to create the list first.
> +      self.kind_to_interfaces[key] = set()
> +      for param in field.kind.fields:
> +        if self._IsPassedInterface(param):
> +          self.kind_to_interfaces[key].add(param)
> +        elif isinstance(param.kind, (module.Struct, module.Union)):
> +          for iface in self._GatherReferencedInterfaces(param):
> +            self.kind_to_interfaces[key].add(iface)
> +    return self.kind_to_interfaces[key]
> +
> +  def _CheckParams(self, method, params):
> +    # Note: we have to repeat _CheckParams for each method as each might have
> +    # different AllowedContext= attributes. We cannot memoize this function,
> +    # but can do so for gathering referenced interfaces as their RequireContext
> +    # attributes do not change.
> +    for param in params:
> +      if self._IsPassedInterface(param):
> +        self._CheckInterface(method, param)
> +      elif isinstance(param.kind, (module.Struct, module.Union)):
> +        for interface in self._GatherReferencedInterfaces(param):
> +          self._CheckInterface(method, interface)
> +
> +  def _CheckMethod(self, method):
> +    if method.parameters:
> +      self._CheckParams(method, method.parameters)
> +    if method.response_parameters:
> +      self._CheckParams(method, method.response_parameters)
> +
> +  def CheckModule(self):
> +    for interface in self.module.interfaces:
> +      for method in interface.methods:
> +        self._CheckMethod(method)
> diff --git a/utils/ipc/mojo/public/tools/bindings/checks/mojom_restrictions_checks_unittest.py b/utils/ipc/mojo/public/tools/bindings/checks/mojom_restrictions_checks_unittest.py
> new file mode 100644
> index 000000000000..a6cd71e2f1f1
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/bindings/checks/mojom_restrictions_checks_unittest.py
> @@ -0,0 +1,254 @@
> +# Copyright 2022 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +
> +import unittest
> +
> +import mojom.generate.check as check
> +from mojom_bindings_generator import LoadChecks, _Generate
> +from mojom_parser_test_case import MojomParserTestCase
> +
> +# Mojoms that we will use in multiple tests.
> +basic_mojoms = {
> +    'level.mojom':
> +    """
> +  module level;
> +  enum Level {
> +    kHighest,
> +    kMiddle,
> +    kLowest,
> +  };
> +  """,
> +    'interfaces.mojom':
> +    """
> +  module interfaces;
> +  import "level.mojom";
> +  struct Foo {int32 bar;};
> +  [RequireContext=level.Level.kHighest]
> +  interface High {
> +    DoFoo(Foo foo);
> +  };
> +  [RequireContext=level.Level.kMiddle]
> +  interface Mid {
> +    DoFoo(Foo foo);
> +  };
> +  [RequireContext=level.Level.kLowest]
> +  interface Low {
> +    DoFoo(Foo foo);
> +  };
> +  """
> +}
> +
> +
> +class FakeArgs:
> +  """Fakes args to _Generate - intention is to do just enough to run checks"""
> +
> +  def __init__(self, tester, files=None):
> +    """ `tester` is MojomParserTestCase for paths.
> +        `files` will have tester path added."""
> +    self.checks_string = 'restrictions'
> +    self.depth = tester.GetPath('')
> +    self.filelist = None
> +    self.filename = [tester.GetPath(x) for x in files]
> +    self.gen_directories = tester.GetPath('gen')
> +    self.generators_string = ''
> +    self.import_directories = []
> +    self.output_dir = tester.GetPath('out')
> +    self.scrambled_message_id_salt_paths = None
> +    self.typemaps = []
> +    self.variant = 'none'
> +
> +
> +class MojoBindingsCheckTest(MojomParserTestCase):
> +  def _WriteBasicMojoms(self):
> +    for filename, contents in basic_mojoms.items():
> +      self.WriteFile(filename, contents)
> +    return list(basic_mojoms.keys())
> +
> +  def _ParseAndGenerate(self, mojoms):
> +    self.ParseMojoms(mojoms)
> +    args = FakeArgs(self, files=mojoms)
> +    _Generate(args, {})
> +
> +  def testLoads(self):
> +    """Validate that the check is registered under the expected name."""
> +    check_modules = LoadChecks('restrictions')
> +    self.assertTrue(check_modules['restrictions'])
> +
> +  def testValidAnnotations(self):
> +    mojoms = self._WriteBasicMojoms()
> +
> +    a = 'a.mojom'
> +    self.WriteFile(
> +        a, """
> +      module a;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +
> +      interface PassesHigh {
> +        [AllowedContext=level.Level.kHighest]
> +        DoHigh(pending_receiver<interfaces.High> hi);
> +      };
> +      interface PassesMedium {
> +        [AllowedContext=level.Level.kMiddle]
> +        DoMedium(pending_receiver<interfaces.Mid> hi);
> +        [AllowedContext=level.Level.kMiddle]
> +        DoMediumRem(pending_remote<interfaces.Mid> hi);
> +        [AllowedContext=level.Level.kMiddle]
> +        DoMediumAssoc(pending_associated_receiver<interfaces.Mid> hi);
> +        [AllowedContext=level.Level.kMiddle]
> +        DoMediumAssocRem(pending_associated_remote<interfaces.Mid> hi);
> +      };
> +      interface PassesLow {
> +        [AllowedContext=level.Level.kLowest]
> +        DoLow(pending_receiver<interfaces.Low> hi);
> +      };
> +
> +      struct One { pending_receiver<interfaces.High> hi; };
> +      struct Two { One one; };
> +      interface PassesNestedHigh {
> +        [AllowedContext=level.Level.kHighest]
> +        DoNestedHigh(Two two);
> +      };
> +
> +      // Allowed as PassesHigh is not itself restricted.
> +      interface PassesPassesHigh {
> +        DoPass(pending_receiver<PassesHigh> hiho);
> +      };
> +    """)
> +    mojoms.append(a)
> +    self._ParseAndGenerate(mojoms)
> +
> +  def _testThrows(self, filename, content, regexp):
> +    mojoms = self._WriteBasicMojoms()
> +    self.WriteFile(filename, content)
> +    mojoms.append(filename)
> +    with self.assertRaisesRegexp(check.CheckException, regexp):
> +      self._ParseAndGenerate(mojoms)
> +
> +  def testMissingAnnotation(self):
> +    contents = """
> +      module b;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +
> +      interface PassesHigh {
> +        // err: missing annotation.
> +        DoHigh(pending_receiver<interfaces.High> hi);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents, 'require.*?AllowedContext')
> +
> +  def testAllowTooLow(self):
> +    contents = """
> +      module b;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +
> +      interface PassesHigh {
> +        // err: level is worse than required.
> +        [AllowedContext=level.Level.kMiddle]
> +        DoHigh(pending_receiver<interfaces.High> hi);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents,
> +                     'RequireContext=.*?kHighest > AllowedContext=.*?kMiddle')
> +
> +  def testWrongEnumInAllow(self):
> +    contents = """
> +      module b;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +      enum Blah {
> +        kZero,
> +      };
> +      interface PassesHigh {
> +        // err: different enums.
> +        [AllowedContext=Blah.kZero]
> +        DoHigh(pending_receiver<interfaces.High> hi);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents, 'but one of kind')
> +
> +  def testNotAnEnumInAllow(self):
> +    contents = """
> +      module b;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +      interface PassesHigh {
> +        // err: not an enum.
> +        [AllowedContext=doopdedoo.mojom.kWhatever]
> +        DoHigh(pending_receiver<interfaces.High> hi);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents, 'not a valid enum value')
> +
> +  def testMissingAllowedForNestedStructs(self):
> +    contents = """
> +      module b;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +      struct One { pending_receiver<interfaces.High> hi; };
> +      struct Two { One one; };
> +      interface PassesNestedHigh {
> +        // err: missing annotation.
> +        DoNestedHigh(Two two);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents, 'require.*?AllowedContext')
> +
> +  def testMissingAllowedForNestedUnions(self):
> +    contents = """
> +      module b;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +      struct One { pending_receiver<interfaces.High> hi; };
> +      struct Two { One one; };
> +      union Three {One one; Two two; };
> +      interface PassesNestedHigh {
> +        // err: missing annotation.
> +        DoNestedHigh(Three three);
> +      };
> +    """
> +    self._testThrows('b.mojom', contents, 'require.*?AllowedContext')
> +
> +  def testMultipleInterfacesThrows(self):
> +    contents = """
> +      module b;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +      struct One { pending_receiver<interfaces.High> hi; };
> +      interface PassesMultipleInterfaces {
> +        [AllowedContext=level.Level.kMiddle]
> +        DoMultiple(
> +          pending_remote<interfaces.Mid> mid,
> +          pending_receiver<interfaces.High> hi,
> +          One one
> +        );
> +      };
> +    """
> +    self._testThrows('b.mojom', contents,
> +                     'RequireContext=.*?kHighest > AllowedContext=.*?kMiddle')
> +
> +  def testMultipleInterfacesAllowed(self):
> +    """Multiple interfaces can be passed, all satisfy the level."""
> +    mojoms = self._WriteBasicMojoms()
> +
> +    b = "b.mojom"
> +    self.WriteFile(
> +        b, """
> +      module b;
> +      import "level.mojom";
> +      import "interfaces.mojom";
> +      struct One { pending_receiver<interfaces.High> hi; };
> +      interface PassesMultipleInterfaces {
> +        [AllowedContext=level.Level.kHighest]
> +        DoMultiple(
> +          pending_receiver<interfaces.High> hi,
> +          pending_remote<interfaces.Mid> mid,
> +          One one
> +        );
> +      };
> +    """)
> +    mojoms.append(b)
> +    self._ParseAndGenerate(mojoms)
> diff --git a/utils/ipc/mojo/public/tools/bindings/chromium_bindings_configuration.gni b/utils/ipc/mojo/public/tools/bindings/chromium_bindings_configuration.gni
> deleted file mode 100644
> index d8a138744856..000000000000
> --- a/utils/ipc/mojo/public/tools/bindings/chromium_bindings_configuration.gni
> +++ /dev/null
> @@ -1,51 +0,0 @@
> -# Copyright 2016 The Chromium Authors. All rights reserved.
> -# Use of this source code is governed by a BSD-style license that can be
> -# found in the LICENSE file.
> -
> -_typemap_imports = [
> -  "//chrome/chrome_cleaner/mojom/typemaps/typemaps.gni",
> -  "//chrome/common/importer/typemaps.gni",
> -  "//chrome/common/media_router/mojom/typemaps.gni",
> -  "//chrome/typemaps.gni",
> -  "//chromecast/typemaps.gni",
> -  "//chromeos/typemaps.gni",
> -  "//chromeos/components/multidevice/mojom/typemaps.gni",
> -  "//chromeos/services/cros_healthd/public/mojom/typemaps.gni",
> -  "//chromeos/services/device_sync/public/mojom/typemaps.gni",
> -  "//chromeos/services/network_config/public/mojom/typemaps.gni",
> -  "//chromeos/services/secure_channel/public/mojom/typemaps.gni",
> -  "//components/arc/mojom/typemaps.gni",
> -  "//components/chromeos_camera/common/typemaps.gni",
> -  "//components/services/storage/public/cpp/filesystem/typemaps.gni",
> -  "//components/sync/mojom/typemaps.gni",
> -  "//components/typemaps.gni",
> -  "//content/browser/typemaps.gni",
> -  "//content/public/common/typemaps.gni",
> -  "//sandbox/mac/mojom/typemaps.gni",
> -  "//services/media_session/public/cpp/typemaps.gni",
> -  "//services/proxy_resolver/public/cpp/typemaps.gni",
> -  "//services/resource_coordinator/public/cpp/typemaps.gni",
> -  "//services/service_manager/public/cpp/typemaps.gni",
> -  "//services/tracing/public/mojom/typemaps.gni",
> -]
> -
> -_typemaps = []
> -foreach(typemap_import, _typemap_imports) {
> -  # Avoid reassignment error by assigning to empty scope first.
> -  _imported = {
> -  }
> -  _imported = read_file(typemap_import, "scope")
> -  _typemaps += _imported.typemaps
> -}
> -
> -typemaps = []
> -foreach(typemap, _typemaps) {
> -  typemaps += [
> -    {
> -      filename = typemap
> -      config = read_file(typemap, "scope")
> -    },
> -  ]
> -}
> -
> -component_macro_suffix = ""
> diff --git a/utils/ipc/mojo/public/tools/bindings/compile_typescript.py b/utils/ipc/mojo/public/tools/bindings/compile_typescript.py
> deleted file mode 100644
> index a978901bc033..000000000000
> --- a/utils/ipc/mojo/public/tools/bindings/compile_typescript.py
> +++ /dev/null
> @@ -1,27 +0,0 @@
> -# Copyright 2019 The Chromium Authors. All rights reserved.
> -# Use of this source code is governed by a BSD-style license that can be
> -# found in the LICENSE file.
> -
> -import os
> -import sys
> -import argparse
> -
> -_HERE_PATH = os.path.dirname(__file__)
> -_SRC_PATH = os.path.normpath(os.path.join(_HERE_PATH, '..', '..', '..', '..'))
> -
> -sys.path.append(os.path.join(_SRC_PATH, 'third_party', 'node'))
> -import node
> -import node_modules
> -
> -def main(argv):
> -  parser = argparse.ArgumentParser()
> -  parser.add_argument('--tsconfig_path', required=True)
> -  args = parser.parse_args(argv)
> -
> -  result = node.RunNode([node_modules.PathToTypescript()] +
> -                        ['--project', args.tsconfig_path])
> -  if len(result) != 0:
> -    raise RuntimeError('Failed to compile Typescript: \n%s' % result)
> -
> -if __name__ == '__main__':
> -  main(sys.argv[1:])
> diff --git a/utils/ipc/mojo/public/tools/bindings/concatenate-files.py b/utils/ipc/mojo/public/tools/bindings/concatenate-files.py
> index 48bc66fd0f6e..4dd26d4aea8b 100755
> --- a/utils/ipc/mojo/public/tools/bindings/concatenate-files.py
> +++ b/utils/ipc/mojo/public/tools/bindings/concatenate-files.py
> @@ -1,5 +1,5 @@
>  #!/usr/bin/env python
> -# Copyright 2019 The Chromium Authors. All rights reserved.
> +# Copyright 2019 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  #
> @@ -15,6 +15,7 @@
>  from __future__ import print_function
>  
>  import optparse
> +import sys
>  
>  
>  def Concatenate(filenames):
> @@ -47,7 +48,7 @@ def main():
>    parser.set_usage("""Concatenate several files into one.
>        Equivalent to: cat file1 ... > target.""")
>    (_options, args) = parser.parse_args()
> -  exit(0 if Concatenate(args) else 1)
> +  sys.exit(0 if Concatenate(args) else 1)
>  
>  
>  if __name__ == "__main__":
> diff --git a/utils/ipc/mojo/public/tools/bindings/concatenate_and_replace_closure_exports.py b/utils/ipc/mojo/public/tools/bindings/concatenate_and_replace_closure_exports.py
> index be8985cedc99..7d56c9f962c3 100755
> --- a/utils/ipc/mojo/public/tools/bindings/concatenate_and_replace_closure_exports.py
> +++ b/utils/ipc/mojo/public/tools/bindings/concatenate_and_replace_closure_exports.py
> @@ -1,5 +1,5 @@
>  #!/usr/bin/env python
> -# Copyright 2018 The Chromium Authors. All rights reserved.
> +# Copyright 2018 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -20,6 +20,7 @@ from __future__ import print_function
>  
>  import optparse
>  import re
> +import sys
>  
>  
>  _MOJO_INTERNAL_MODULE_NAME = "mojo.internal"
> @@ -31,10 +32,10 @@ def FilterLine(filename, line, output):
>      return
>  
>    if line.startswith("goog.provide"):
> -    match = re.match("goog.provide\('([^']+)'\);", line)
> +    match = re.match(r"goog.provide\('([^']+)'\);", line)
>      if not match:
>        print("Invalid goog.provide line in %s:\n%s" % (filename, line))
> -      exit(1)
> +      sys.exit(1)
>  
>      module_name = match.group(1)
>      if module_name == _MOJO_INTERNAL_MODULE_NAME:
> @@ -67,7 +68,8 @@ def main():
>      Concatenate several files into one, stripping Closure provide and
>      require directives along the way.""")
>    (_, args) = parser.parse_args()
> -  exit(0 if ConcatenateAndReplaceExports(args) else 1)
> +  sys.exit(0 if ConcatenateAndReplaceExports(args) else 1)
> +
>  
>  if __name__ == "__main__":
>    main()
> diff --git a/utils/ipc/mojo/public/tools/bindings/format_typemap_generator_args.py b/utils/ipc/mojo/public/tools/bindings/format_typemap_generator_args.py
> deleted file mode 100755
> index 7ac4af5faef1..000000000000
> --- a/utils/ipc/mojo/public/tools/bindings/format_typemap_generator_args.py
> +++ /dev/null
> @@ -1,36 +0,0 @@
> -#!/usr/bin/env python
> -# Copyright 2016 The Chromium Authors. All rights reserved.
> -# Use of this source code is governed by a BSD-style license that can be
> -# found in the LICENSE file.
> -
> -from __future__ import print_function
> -
> -import sys
> -
> -# This utility converts mojom dependencies into their corresponding typemap
> -# paths and formats them to be consumed by generate_type_mappings.py.
> -
> -
> -def FormatTypemap(typemap_filename):
> -  # A simple typemap is valid Python with a minor alteration.
> -  with open(typemap_filename) as f:
> -    typemap_content = f.read().replace('=\n', '=')
> -  typemap = {}
> -  exec typemap_content in typemap
> -
> -  for header in typemap.get('public_headers', []):
> -    yield 'public_headers=%s' % header
> -  for header in typemap.get('traits_headers', []):
> -    yield 'traits_headers=%s' % header
> -  for header in typemap.get('type_mappings', []):
> -    yield 'type_mappings=%s' % header
> -
> -
> -def main():
> -  typemaps = sys.argv[1:]
> -  print(' '.join('--start-typemap %s' % ' '.join(FormatTypemap(typemap))
> -                 for typemap in typemaps))
> -
> -
> -if __name__ == '__main__':
> -  sys.exit(main())
> diff --git a/utils/ipc/mojo/public/tools/bindings/gen_data_files_list.py b/utils/ipc/mojo/public/tools/bindings/gen_data_files_list.py
> index 8b78d0924185..c6daff034f7c 100644
> --- a/utils/ipc/mojo/public/tools/bindings/gen_data_files_list.py
> +++ b/utils/ipc/mojo/public/tools/bindings/gen_data_files_list.py
> @@ -1,4 +1,4 @@
> -# Copyright 2017 The Chromium Authors. All rights reserved.
> +# Copyright 2017 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Generates a list of all files in a directory.
> diff --git a/utils/ipc/mojo/public/tools/bindings/generate_type_mappings.py b/utils/ipc/mojo/public/tools/bindings/generate_type_mappings.py
> index a009664945fe..4a53e2bffe1e 100755
> --- a/utils/ipc/mojo/public/tools/bindings/generate_type_mappings.py
> +++ b/utils/ipc/mojo/public/tools/bindings/generate_type_mappings.py
> @@ -1,5 +1,5 @@
>  #!/usr/bin/env python
> -# Copyright 2016 The Chromium Authors. All rights reserved.
> +# Copyright 2016 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Generates a JSON typemap from its command-line arguments and dependencies.
> @@ -82,10 +82,12 @@ def LoadCppTypemapConfig(path):
>        for entry in config['types']:
>          configs[entry['mojom']] = {
>              'typename': entry['cpp'],
> +            'forward_declaration': entry.get('forward_declaration', None),
>              'public_headers': config.get('traits_headers', []),
>              'traits_headers': config.get('traits_private_headers', []),
>              'copyable_pass_by_value': entry.get('copyable_pass_by_value',
>                                                  False),
> +            'default_constructible': entry.get('default_constructible', True),
>              'force_serialize': entry.get('force_serialize', False),
>              'hashable': entry.get('hashable', False),
>              'move_only': entry.get('move_only', False),
> diff --git a/utils/ipc/mojo/public/tools/bindings/minify_with_terser.py b/utils/ipc/mojo/public/tools/bindings/minify_with_terser.py
> new file mode 100755
> index 000000000000..cefee7a401a6
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/bindings/minify_with_terser.py
> @@ -0,0 +1,47 @@
> +#!/usr/bin/env python3
> +# Copyright 2023 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +#
> +# This utility minifies JS files with terser.
> +#
> +# Instance of 'node' has no 'RunNode' member (no-member)
> +# pylint: disable=no-member
> +
> +import argparse
> +import os
> +import sys
> +
> +_HERE_PATH = os.path.dirname(__file__)
> +_SRC_PATH = os.path.normpath(os.path.join(_HERE_PATH, '..', '..', '..', '..'))
> +_CWD = os.getcwd()
> +sys.path.append(os.path.join(_SRC_PATH, 'third_party', 'node'))
> +import node
> +import node_modules
> +
> +
> +def MinifyFile(input_file, output_file):
> +  node.RunNode([
> +      node_modules.PathToTerser(), input_file, '--mangle', '--compress',
> +      '--comments', 'false', '--output', output_file
> +  ])
> +
> +
> +def main(argv):
> +  parser = argparse.ArgumentParser()
> +  parser.add_argument('--input', required=True)
> +  parser.add_argument('--output', required=True)
> +  args = parser.parse_args(argv)
> +
> +  # Delete the output file if it already exists. It may be a sym link to the
> +  # input, because in non-optimized/pre-Terser builds the input file is copied
> +  # to the output location with gn copy().
> +  out_path = os.path.join(_CWD, args.output)
> +  if (os.path.exists(out_path)):
> +    os.remove(out_path)
> +
> +  MinifyFile(os.path.join(_CWD, args.input), out_path)
> +
> +
> +if __name__ == '__main__':
> +  main(sys.argv[1:])
> diff --git a/utils/ipc/mojo/public/tools/bindings/mojom.gni b/utils/ipc/mojo/public/tools/bindings/mojom.gni
> index fe2a1da3750a..3f6e54e0a315 100644
> --- a/utils/ipc/mojo/public/tools/bindings/mojom.gni
> +++ b/utils/ipc/mojo/public/tools/bindings/mojom.gni
> @@ -1,25 +1,28 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import("//build/config/python.gni")
>  import("//third_party/closure_compiler/closure_args.gni")
>  import("//third_party/closure_compiler/compile_js.gni")
>  import("//third_party/protobuf/proto_library.gni")
> +import("//ui/webui/resources/tools/generate_grd.gni")
>  import("//ui/webui/webui_features.gni")
>  
> +import("//build/config/cast.gni")
> +
>  # TODO(rockot): Maybe we can factor these dependencies out of //mojo. They're
>  # used to conditionally enable message ID scrambling in a way which is
>  # consistent across toolchains and which is affected by branded vs non-branded
>  # Chrome builds. Ideally we could create some generic knobs here that could be
>  # flipped elsewhere though.
>  import("//build/config/chrome_build.gni")
> -import("//build/config/chromecast_build.gni")
>  import("//build/config/chromeos/ui_mode.gni")
> +import("//build/config/features.gni")
>  import("//build/config/nacl/config.gni")
>  import("//build/toolchain/kythe.gni")
>  import("//components/nacl/features.gni")
>  import("//third_party/jinja2/jinja2.gni")
> +import("//third_party/ply/ply.gni")
>  import("//tools/ipc_fuzzer/ipc_fuzzer.gni")
>  declare_args() {
>    # Indicates whether typemapping should be supported in this build
> @@ -34,21 +37,30 @@ declare_args() {
>  
>    # Controls message ID scrambling behavior. If |true|, message IDs are
>    # scrambled (i.e. randomized based on the contents of //chrome/VERSION) on
> -  # non-Chrome OS desktop platforms. Set to |false| to disable message ID
> -  # scrambling on all platforms.
> -  enable_mojom_message_id_scrambling = true
> -
> -  # Enables Closure compilation of generated JS lite bindings. In environments
> -  # where compilation is supported, any mojom target "foo" will also have a
> -  # corresponding "foo_js_library_for_compile" target generated.
> -  enable_mojom_closure_compile = enable_js_type_check && optimize_webui
> -
> -  # Enables generating Typescript bindings and compiling them to JS bindings.
> -  enable_typescript_bindings = false
> +  # non-Chrome OS desktop platforms. Enabled on official builds by default.
> +  # Set to |true| to enable message ID scrambling on a specific build.
> +  # See also `enable_scrambled_message_ids` below for more details.
> +  enable_mojom_message_id_scrambling = is_official_build
>  
>    # Enables generating javascript fuzzing-related code and the bindings for the
>    # MojoLPM fuzzer targets. Off by default.
>    enable_mojom_fuzzer = false
> +
> +  # Enables Closure compilation of generated JS lite bindings. In environments
> +  # where compilation is supported, any mojom target "foo" will also have a
> +  # corresponding "foo_js_library_for_compile" target generated.
> +  if (is_chromeos_ash) {
> +    enable_mojom_closure_compile = enable_js_type_check && optimize_webui
> +  }
> +}
> +
> +# Closure libraries are needed for mojom_closure_compile, and when
> +# js_type_check is enabled on Ash.
> +if (is_chromeos_ash) {
> +  generate_mojom_closure_libraries =
> +      enable_mojom_closure_compile || enable_js_type_check
> +} else {
> +  generate_mojom_closure_libraries = false
>  }
>  
>  # NOTE: We would like to avoid scrambling message IDs where it doesn't add
> @@ -69,9 +81,8 @@ declare_args() {
>  # lacros-chrome switches to target_os="chromeos"
>  enable_scrambled_message_ids =
>      enable_mojom_message_id_scrambling &&
> -    (is_mac || is_win ||
> -     (is_linux && !is_chromeos_ash && !is_chromecast && !is_chromeos_lacros) ||
> -     ((enable_nacl || is_nacl || is_nacl_nonsfi) &&
> +    (is_mac || is_win || (is_linux && !is_castos) ||
> +     ((enable_nacl || is_nacl) &&
>        (target_os != "chromeos" && !chromeos_is_browser_only)))
>  
>  _mojom_tools_root = "//mojo/public/tools"
> @@ -80,7 +91,9 @@ mojom_parser_script = "$_mojom_tools_root/mojom/mojom_parser.py"
>  mojom_parser_sources = [
>    "$_mojom_library_root/__init__.py",
>    "$_mojom_library_root/error.py",
> +  "$_mojom_library_root/fileutil.py",
>    "$_mojom_library_root/generate/__init__.py",
> +  "$_mojom_library_root/generate/check.py",
>    "$_mojom_library_root/generate/generator.py",
>    "$_mojom_library_root/generate/module.py",
>    "$_mojom_library_root/generate/pack.py",
> @@ -88,21 +101,32 @@ mojom_parser_sources = [
>    "$_mojom_library_root/generate/translate.py",
>    "$_mojom_library_root/parse/__init__.py",
>    "$_mojom_library_root/parse/ast.py",
> +  "$_mojom_library_root/parse/conditional_features.py",
>    "$_mojom_library_root/parse/lexer.py",
>    "$_mojom_library_root/parse/parser.py",
> +  "//tools/diagnosis/crbug_1001171.py",
>  ]
>  
>  mojom_generator_root = "$_mojom_tools_root/bindings"
>  mojom_generator_script = "$mojom_generator_root/mojom_bindings_generator.py"
>  mojom_generator_sources =
>      mojom_parser_sources + [
> +      "$mojom_generator_root/checks/__init__.py",
> +      "$mojom_generator_root/checks/mojom_attributes_check.py",
> +      "$mojom_generator_root/checks/mojom_definitions_check.py",
> +      "$mojom_generator_root/checks/mojom_interface_feature_check.py",
> +      "$mojom_generator_root/checks/mojom_restrictions_check.py",
> +      "$mojom_generator_root/generators/__init__.py",
>        "$mojom_generator_root/generators/cpp_util.py",
>        "$mojom_generator_root/generators/mojom_cpp_generator.py",
>        "$mojom_generator_root/generators/mojom_java_generator.py",
> -      "$mojom_generator_root/generators/mojom_mojolpm_generator.py",
>        "$mojom_generator_root/generators/mojom_js_generator.py",
> +      "$mojom_generator_root/generators/mojom_mojolpm_generator.py",
>        "$mojom_generator_root/generators/mojom_ts_generator.py",
>        "$mojom_generator_script",
> +      "//build/action_helpers.py",
> +      "//build/gn_helpers.py",
> +      "//build/zip_helpers.py",
>      ]
>  
>  if (enable_scrambled_message_ids) {
> @@ -243,12 +267,16 @@ if (enable_scrambled_message_ids) {
>  #       |cpp_only| is set to true, it overrides this to prevent generation of
>  #       Java bindings.
>  #
> -#   enable_fuzzing (optional)
> +#   enable_js_fuzzing (optional)
> +#       Enables generation of javascript fuzzing sources for the target if the
> +#       global build arg |enable_mojom_fuzzer| is also set to |true|.
> +#       Defaults to |true|. If JS fuzzing generation is enabled for a target,
> +#       the target will always generate JS bindings even if |cpp_only| is set to
> +#       |true|. See note above.
> +#
> +#   enable_mojolpm_fuzzing (optional)
>  #       Enables generation of fuzzing sources for the target if the global build
> -#       arg |enable_mojom_fuzzer| is also set to |true|. Defaults to |true|. If
> -#       fuzzing generation is enabled for a target, the target will always
> -#       generate JS bindings even if |cpp_only| is set to |true|. See note
> -#       above.
> +#       arg |enable_mojom_fuzzer| is also set to |true|. Defaults to |true|.
>  #
>  #   support_lazy_serialization (optional)
>  #       If set to |true|, generated C++ bindings will effectively prefer to
> @@ -310,8 +338,15 @@ if (enable_scrambled_message_ids) {
>  #       correct dependency order. Note that this only has an effect if
>  #       the |enable_mojom_closure_compile| global arg is set to |true| as well.
>  #
> -#   use_typescript_sources (optional)
> -#       Uses the Typescript generator to generate JavaScript bindings.
> +#   generate_webui_js_bindings (optional)
> +#       Generate WebUI bindings in JavaScript rather than TypeScript. Defaults
> +#       to false. ChromeOS only parameter.
> +#
> +#   generate_legacy_js_bindings (optional)
> +#       Generate js_data_deps target containing legacy JavaScript bindings files
> +#       for Blink tests and other non-WebUI users when generating TypeScript
> +#       bindings for WebUI. Ignored if generate_webui_js_bindings is set to
> +#       true.
>  #
>  #   js_generate_struct_deserializers (optional)
>  #       Generates JS deerialize methods for structs.
> @@ -323,17 +358,23 @@ if (enable_scrambled_message_ids) {
>  #   webui_module_path (optional)
>  #       The path or URL at which modules generated by this target will be
>  #       accessible to WebUI pages. This may either be an absolute path or
> -#       a full URL path starting with "chrome://resources/mojo".
> +#       a full URL path starting with "chrome://resources/mojo". If this path
> +#       is not specified, WebUI bindings will not be generated.
>  #
>  #       If an absolute path, a WebUI page may only import these modules if
> -#       they are manually packaged and mapped independently by that page's
> -#       WebUIDataSource. The mapped path must match the path given here.
> +#       they are added to that page's data source (usually by adding the
> +#       modules to the mojo_files list for build_webui(), or by listing the
> +#       files as inputs to the page's ts_library() and/or generate_grd() build
> +#       steps.
>  #
>  #       If this is is instead a URL string starting with
> -#       "chrome://resources/mojo", the generated resources must be added to
> -#       content_resources.grd and registered with
> -#       content::SharedResourcesDataSource with a corresponding path, at which
> -#       point they will be made available to all WebUI pages at the given URL.
> +#       "chrome://resources/mojo", the resulting bindings files should
> +#       be added to one of the lists in ui/webui/resources/mojo/BUILD.gn,
> +#       at which point they will be made available to all WebUI pages at the
> +#       given URL.
> +#
> +#       Note: WebUI module bindings are generated in TypeScript by default,
> +#       unless |generate_webui_js_bindings| is specified as true.
>  #
>  # The following parameters are used to support the component build. They are
>  # needed so that bindings which are linked with a component can use the same
> @@ -402,16 +443,41 @@ if (enable_scrambled_message_ids) {
>  #             should be mapped in generated bindings. This is a string like
>  #             "::base::Value" or "std::vector<::base::Value>".
>  #
> -#         move_only (optional)
> -#             A boolean value (default false) which indicates whether the C++
> -#             type is move-only. If true, generated bindings will pass the type
> -#             by value and use std::move() at call sites.
> -#
>  #         copyable_pass_by_value (optional)
>  #             A boolean value (default false) which effectively indicates
>  #             whether the C++ type is very cheap to copy. If so, generated
>  #             bindings will pass by value but not use std::move() at call sites.
>  #
> +#         default_constructible (optional)
> +#             A boolean value (default true) which indicates whether the C++
> +#             type is default constructible. If a C++ type is not default
> +#             constructible (e.g. the implementor of the type prefers not to
> +#             publicly expose a default constructor that creates an object in an
> +#             invalid state), Mojo will instead construct C++ type with an
> +#             argument of the type `mojo::DefaultConstruct::Tag` (essentially a
> +#             passkey-like type specifically for this use case).
> +#
> +#         force_serialize (optional)
> +#             A boolean value (default false) which disables lazy serialization
> +#             of the typemapped type if lazy serialization is enabled for the
> +#             mojom target applying this typemap.
> +#
> +#         forward_declaration (optional)
> +#             A forward declaration of the C++ type, which bindings that don't
> +#             need the full type definition can use to reduce the size of
> +#             the generated code. This is a string like
> +#             "namespace base { class Value; }".
> +#
> +#         hashable (optional)
> +#             A boolean value (default false) indicating whether the C++ type is
> +#             hashable. Set to true if true AND needed (i.e. you need to use the
> +#             type as the key of a mojom map).
> +#
> +#         move_only (optional)
> +#             A boolean value (default false) which indicates whether the C++
> +#             type is move-only. If true, generated bindings will pass the type
> +#             by value and use std::move() at call sites.
> +#
>  #         nullable_is_same_type (optional)
>  #             A boolean value (default false) which indicates that the C++ type
>  #             has some baked-in semantic notion of a "null" state. If true, the
> @@ -421,16 +487,6 @@ if (enable_scrambled_message_ids) {
>  #             type with absl::optional, and null values are simply
>  #             absl::nullopt.
>  #
> -#         hashable (optional)
> -#             A boolean value (default false) indicating whether the C++ type is
> -#             hashable. Set to true if true AND needed (i.e. you need to use the
> -#             type as the key of a mojom map).
> -#
> -#         force_serialize (optional)
> -#             A boolean value (default false) which disables lazy serialization
> -#             of the typemapped type if lazy serialization is enabled for the
> -#             mojom target applying this typemap.
> -#
>  # Additional typemap scope parameters:
>  #
>  #   traits_headers (optional)
> @@ -621,20 +677,26 @@ template("mojom") {
>    build_metadata_filename = "$target_gen_dir/$target_name.build_metadata"
>    build_metadata = {
>    }
> -  build_metadata.sources = rebase_path(sources_list)
> +  build_metadata.sources = rebase_path(sources_list, target_gen_dir)
>    build_metadata.deps = []
>    foreach(dep, all_deps) {
>      dep_target_gen_dir = get_label_info(dep, "target_gen_dir")
>      dep_name = get_label_info(dep, "name")
>      build_metadata.deps +=
> -        [ rebase_path("$dep_target_gen_dir/$dep_name.build_metadata") ]
> +        [ rebase_path("$dep_target_gen_dir/$dep_name.build_metadata",
> +                      target_gen_dir) ]
>    }
>    write_file(build_metadata_filename, build_metadata, "json")
>  
> -  generate_fuzzing =
> -      (!defined(invoker.enable_fuzzing) || invoker.enable_fuzzing) &&
> +  generate_js_fuzzing =
> +      (!defined(invoker.enable_js_fuzzing) || invoker.enable_js_fuzzing) &&
>        enable_mojom_fuzzer && (!defined(invoker.testonly) || !invoker.testonly)
>  
> +  generate_mojolpm_fuzzing =
> +      (!defined(invoker.enable_mojolpm_fuzzing) ||
> +       invoker.enable_mojolpm_fuzzing) && enable_mojom_fuzzer &&
> +      (!defined(invoker.testonly) || !invoker.testonly)
> +
>    parser_target_name = "${target_name}__parser"
>    parser_deps = []
>    foreach(dep, all_deps) {
> @@ -665,30 +727,34 @@ template("mojom") {
>          "is_chromeos",
>          "is_chromeos_ash",
>        ]
> +    } else if (is_chromeos_lacros) {
> +      enabled_features += [
> +        "is_chromeos",
> +        "is_chromeos_lacros",
> +      ]
>      } else if (is_fuchsia) {
>        enabled_features += [ "is_fuchsia" ]
>      } else if (is_ios) {
>        enabled_features += [ "is_ios" ]
> -    } else if (is_linux || is_chromeos_lacros) {
> +    } else if (is_linux) {
>        enabled_features += [ "is_linux" ]
> -      if (is_chromeos_lacros) {
> -        enabled_features += [
> -          "is_chromeos",
> -          "is_chromeos_lacros",
> -        ]
> -      }
>      } else if (is_mac) {
>        enabled_features += [ "is_mac" ]
>      } else if (is_win) {
>        enabled_features += [ "is_win" ]
>      }
>  
> -    # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -    python2_action(parser_target_name) {
> +    if (is_apple) {
> +      enabled_features += [ "is_apple" ]
> +    }
> +
> +    action(parser_target_name) {
> +      allow_remote = true
> +      custom_processor = "mojom_parser"
>        script = mojom_parser_script
> -      inputs = mojom_parser_sources + [ build_metadata_filename ]
> +      inputs = mojom_parser_sources + ply_sources + [ build_metadata_filename ]
>        sources = sources_list
> -      deps = parser_deps
> +      public_deps = parser_deps
>        outputs = []
>        foreach(base_path, output_file_base_paths) {
>          filename = get_path_info(base_path, "file")
> @@ -698,31 +764,35 @@ template("mojom") {
>  
>        filelist = []
>        foreach(source, sources_list) {
> -        filelist += [ rebase_path(source) ]
> +        filelist += [ rebase_path(source, root_build_dir) ]
>        }
> -      response_file_contents = filelist
> +
> +      # Workaround for https://github.com/ninja-build/ninja/issues/1966.
> +      rsp_file = "$target_gen_dir/${target_name}.rsp"
> +      write_file(rsp_file, filelist)
> +      inputs += [ rsp_file ]
>  
>        args = [
>          # Resolve relative input mojom paths against both the root src dir and
>          # the root gen dir.
>          "--input-root",
> -        rebase_path("//."),
> +        rebase_path("//.", root_build_dir),
>          "--input-root",
> -        rebase_path(root_gen_dir),
> +        rebase_path(root_gen_dir, root_build_dir),
>  
>          "--output-root",
> -        rebase_path(root_gen_dir),
> +        rebase_path(root_gen_dir, root_build_dir),
>  
> -        "--mojom-file-list={{response_file_name}}",
> +        "--mojom-file-list=" + rebase_path(rsp_file, root_build_dir),
>  
>          "--check-imports",
> -        rebase_path(build_metadata_filename),
> +        rebase_path(build_metadata_filename, root_build_dir),
>        ]
>  
>        if (defined(invoker.input_root_override)) {
>          args += [
>            "--input-root",
> -          rebase_path(invoker.input_root_override),
> +          rebase_path(invoker.input_root_override, root_build_dir),
>          ]
>        }
>  
> @@ -738,6 +808,13 @@ template("mojom") {
>            "--add-module-metadata",
>            "webui_module_path=${invoker.webui_module_path}",
>          ]
> +        if (defined(invoker.generate_webui_js_bindings) &&
> +            invoker.generate_webui_js_bindings) {
> +          args += [
> +            "--add-module-metadata",
> +            "generate_webui_js=True",
> +          ]
> +        }
>        }
>      }
>    }
> @@ -819,11 +896,12 @@ template("mojom") {
>        }
>      }
>  
> -    # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -    python2_action(generator_cpp_message_ids_target_name) {
> +    action(generator_cpp_message_ids_target_name) {
> +      allow_remote = true
>        script = mojom_generator_script
>        inputs = mojom_generator_sources + jinja2_sources
> -      sources = sources_list
> +      sources = sources_list +
> +                [ "$root_gen_dir/mojo/public/tools/bindings/cpp_templates.zip" ]
>        deps = [
>          ":$parser_target_name",
>          "//mojo/public/tools/bindings:precompile_templates",
> @@ -835,16 +913,22 @@ template("mojom") {
>        args = common_generator_args
>        filelist = []
>        foreach(source, sources_list) {
> -        filelist += [ rebase_path("$source", root_build_dir) ]
> +        filelist += [ rebase_path(source, root_build_dir) ]
>        }
>        foreach(base_path, output_file_base_paths) {
> +        filename = get_path_info(base_path, "file")
> +        dirname = get_path_info(base_path, "dir")
> +        inputs += [ "$root_gen_dir/$dirname/${filename}-module" ]
>          outputs += [ "$root_gen_dir/$base_path-shared-message-ids.h" ]
>        }
>  
> -      response_file_contents = filelist
> +      # Workaround for https://github.com/ninja-build/ninja/issues/1966.
> +      rsp_file = "$target_gen_dir/${target_name}.rsp"
> +      write_file(rsp_file, filelist)
> +      inputs += [ rsp_file ]
>  
>        args += [
> -        "--filelist={{response_file_name}}",
> +        "--filelist=" + rebase_path(rsp_file, root_build_dir),
>          "--generate_non_variant_code",
>          "--generate_message_ids",
>          "-g",
> @@ -860,12 +944,13 @@ template("mojom") {
>  
>      generator_shared_target_name = "${target_name}_shared__generator"
>  
> -    # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -    python2_action(generator_shared_target_name) {
> +    action(generator_shared_target_name) {
> +      allow_remote = true
>        visibility = [ ":*" ]
>        script = mojom_generator_script
>        inputs = mojom_generator_sources + jinja2_sources
> -      sources = sources_list
> +      sources = sources_list +
> +                [ "$root_gen_dir/mojo/public/tools/bindings/cpp_templates.zip" ]
>        deps = [
>          ":$parser_target_name",
>          "//mojo/public/tools/bindings:precompile_templates",
> @@ -878,10 +963,16 @@ template("mojom") {
>        args = common_generator_args
>        filelist = []
>        foreach(source, sources_list) {
> -        filelist += [ rebase_path("$source", root_build_dir) ]
> +        filelist += [ rebase_path(source, root_build_dir) ]
>        }
>        foreach(base_path, output_file_base_paths) {
> +        # Need the mojom-module as an input to this action.
> +        filename = get_path_info(base_path, "file")
> +        dirname = get_path_info(base_path, "dir")
> +        inputs += [ "$root_gen_dir/$dirname/${filename}-module" ]
> +
>          outputs += [
> +          "$root_gen_dir/$base_path-features.h",
>            "$root_gen_dir/$base_path-params-data.h",
>            "$root_gen_dir/$base_path-shared-internal.h",
>            "$root_gen_dir/$base_path-shared.cc",
> @@ -889,10 +980,13 @@ template("mojom") {
>          ]
>        }
>  
> -      response_file_contents = filelist
> +      # Workaround for https://github.com/ninja-build/ninja/issues/1966.
> +      rsp_file = "$target_gen_dir/${target_name}.rsp"
> +      write_file(rsp_file, filelist)
> +      inputs += [ rsp_file ]
>  
>        args += [
> -        "--filelist={{response_file_name}}",
> +        "--filelist=" + rebase_path(rsp_file, root_build_dir),
>          "--generate_non_variant_code",
>          "-g",
>          "c++",
> @@ -923,12 +1017,14 @@ template("mojom") {
>      if (defined(invoker.testonly)) {
>        testonly = invoker.testonly
>      }
> +    configs += [ "//build/config/compiler:wexit_time_destructors" ]
>      deps = []
>      public_deps = []
>      if (output_file_base_paths != []) {
>        sources = []
>        foreach(base_path, output_file_base_paths) {
>          sources += [
> +          "$root_gen_dir/$base_path-features.h",
>            "$root_gen_dir/$base_path-params-data.h",
>            "$root_gen_dir/$base_path-shared-internal.h",
>            "$root_gen_dir/$base_path-shared.cc",
> @@ -972,7 +1068,7 @@ template("mojom") {
>      }
>    }
>  
> -  if (generate_fuzzing) {
> +  if (generate_mojolpm_fuzzing) {
>      # This block generates the proto files used for the MojoLPM fuzzer,
>      # and the corresponding proto targets that will be linked in the fuzzer
>      # targets. These are independent of the typemappings, and can be done
> @@ -981,11 +1077,15 @@ template("mojom") {
>      generator_mojolpm_proto_target_name =
>          "${target_name}_mojolpm_proto_generator"
>  
> -    # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -    python2_action(generator_mojolpm_proto_target_name) {
> +    action(generator_mojolpm_proto_target_name) {
> +      allow_remote = true
>        script = mojom_generator_script
>        inputs = mojom_generator_sources + jinja2_sources
> -      sources = invoker.sources
> +      sources =
> +          invoker.sources + [
> +            "$root_gen_dir/mojo/public/tools/bindings/cpp_templates.zip",
> +            "$root_gen_dir/mojo/public/tools/bindings/mojolpm_templates.zip",
> +          ]
>        deps = [
>          ":$parser_target_name",
>          "//mojo/public/tools/bindings:precompile_templates",
> @@ -994,15 +1094,37 @@ template("mojom") {
>        outputs = []
>        args = common_generator_args
>        filelist = []
> -      foreach(source, invoker.sources) {
> -        filelist += [ rebase_path("$source", root_build_dir) ]
> +
> +      # Split the input into generated and non-generated source files. They
> +      # need to be processed separately.
> +      gen_dir_path_wildcard = get_path_info("//", "gen_dir") + "/*"
> +      non_gen_sources =
> +          filter_exclude(invoker.sources, [ gen_dir_path_wildcard ])
> +      gen_sources = filter_include(invoker.sources, [ gen_dir_path_wildcard ])
> +
> +      foreach(source, non_gen_sources) {
> +        filelist += [ rebase_path(source, root_build_dir) ]
> +        inputs += [ "$target_gen_dir/$source-module" ]
>          outputs += [ "$target_gen_dir/$source.mojolpm.proto" ]
>        }
>  
> -      response_file_contents = filelist
> +      foreach(source, gen_sources) {
> +        filelist += [ rebase_path(source, root_build_dir) ]
> +
> +        # For generated files, we assume they're in the target_gen_dir or a
> +        # sub-folder of it. Rebase the path so we can get the relative location.
> +        source_file = rebase_path(source, target_gen_dir)
> +        inputs += [ "$target_gen_dir/$source_file-module" ]
> +        outputs += [ "$target_gen_dir/$source_file.mojolpm.proto" ]
> +      }
> +
> +      # Workaround for https://github.com/ninja-build/ninja/issues/1966.
> +      rsp_file = "$target_gen_dir/${target_name}.rsp"
> +      write_file(rsp_file, filelist)
> +      inputs += [ rsp_file ]
>  
>        args += [
> -        "--filelist={{response_file_name}}",
> +        "--filelist=" + rebase_path(rsp_file, root_build_dir),
>          "--generate_non_variant_code",
>          "-g",
>          "mojolpm",
> @@ -1014,9 +1136,20 @@ template("mojom") {
>        proto_library(mojolpm_proto_target_name) {
>          testonly = true
>          generate_python = false
> +
> +        # Split the input into generated and non-generated source files. They
> +        # need to be processed separately.
> +        gen_dir_path_wildcard = get_path_info("//", "gen_dir") + "/*"
> +        non_gen_sources =
> +            filter_exclude(invoker.sources, [ gen_dir_path_wildcard ])
> +        gen_sources = filter_include(invoker.sources, [ gen_dir_path_wildcard ])
>          sources = process_file_template(
> -                invoker.sources,
> +                non_gen_sources,
>                  [ "{{source_gen_dir}}/{{source_file_part}}.mojolpm.proto" ])
> +        sources += process_file_template(
> +                gen_sources,
> +                [ "{{source_dir}}/{{source_file_part}}.mojolpm.proto" ])
> +
>          import_dirs = [ "//" ]
>          proto_in_dir = "${root_gen_dir}"
>          proto_out_dir = "."
> @@ -1055,7 +1188,7 @@ template("mojom") {
>      component_macro_suffix = ""
>    }
>    if ((!defined(invoker.disable_variants) || !invoker.disable_variants) &&
> -      !is_ios) {
> +      use_blink) {
>      blink_variant = {
>        variant = "blink"
>        component_macro_suffix = "_BLINK"
> @@ -1149,39 +1282,6 @@ template("mojom") {
>              "${bindings_configuration.component_macro_suffix}_IMPL" ]
>      }
>  
> -    export_args = []
> -    export_args_overridden = false
> -    if (defined(bindings_configuration.for_blink) &&
> -        bindings_configuration.for_blink) {
> -      if (defined(invoker.export_class_attribute_blink)) {
> -        export_args_overridden = true
> -        export_args += [
> -          "--export_attribute",
> -          invoker.export_class_attribute_blink,
> -          "--export_header",
> -          invoker.export_header_blink,
> -        ]
> -      }
> -    } else if (defined(invoker.export_class_attribute)) {
> -      export_args_overridden = true
> -      export_args += [
> -        "--export_attribute",
> -        invoker.export_class_attribute,
> -        "--export_header",
> -        invoker.export_header,
> -      ]
> -    }
> -
> -    if (!export_args_overridden && defined(invoker.component_macro_prefix)) {
> -      export_args += [
> -        "--export_attribute",
> -        "COMPONENT_EXPORT(${invoker.component_macro_prefix}" +
> -            "${bindings_configuration.component_macro_suffix})",
> -        "--export_header",
> -        "base/component_export.h",
> -      ]
> -    }
> -
>      generate_java = false
>      if (!cpp_only && defined(invoker.generate_java)) {
>        generate_java = invoker.generate_java
> @@ -1190,6 +1290,38 @@ template("mojom") {
>      type_mappings_path =
>          "$target_gen_dir/${target_name}${variant_suffix}__type_mappings"
>      if (sources_list != []) {
> +      export_args = []
> +      export_args_overridden = false
> +      if (defined(bindings_configuration.for_blink) &&
> +          bindings_configuration.for_blink) {
> +        if (defined(invoker.export_class_attribute_blink)) {
> +          export_args_overridden = true
> +          export_args += [
> +            "--export_attribute",
> +            invoker.export_class_attribute_blink,
> +            "--export_header",
> +            invoker.export_header_blink,
> +          ]
> +        }
> +      } else if (defined(invoker.export_class_attribute)) {
> +        export_args_overridden = true
> +        export_args += [
> +          "--export_attribute",
> +          invoker.export_class_attribute,
> +          "--export_header",
> +          invoker.export_header,
> +        ]
> +      }
> +      if (!export_args_overridden && defined(invoker.component_macro_prefix)) {
> +        export_args += [
> +          "--export_attribute",
> +          "COMPONENT_EXPORT(${invoker.component_macro_prefix}" +
> +              "${bindings_configuration.component_macro_suffix})",
> +          "--export_header",
> +          "base/component_export.h",
> +        ]
> +      }
> +
>        generator_cpp_output_suffixes = []
>        variant_dash_suffix = ""
>        if (defined(variant)) {
> @@ -1198,7 +1330,6 @@ template("mojom") {
>        generator_cpp_output_suffixes += [
>          "${variant_dash_suffix}-forward.h",
>          "${variant_dash_suffix}-import-headers.h",
> -        "${variant_dash_suffix}-test-utils.cc",
>          "${variant_dash_suffix}-test-utils.h",
>          "${variant_dash_suffix}.cc",
>          "${variant_dash_suffix}.h",
> @@ -1207,16 +1338,28 @@ template("mojom") {
>        generator_target_name = "${target_name}${variant_suffix}__generator"
>  
>        # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -      python2_action(generator_target_name) {
> +      action(generator_target_name) {
> +        allow_remote = true
>          visibility = [ ":*" ]
>          script = mojom_generator_script
>          inputs = mojom_generator_sources + jinja2_sources
> -        sources = sources_list
> +        sources =
> +            sources_list + [
> +              "$root_gen_dir/mojo/public/tools/bindings/cpp_templates.zip",
> +              type_mappings_path,
> +            ]
> +        if (generate_mojolpm_fuzzing &&
> +            !defined(bindings_configuration.variant)) {
> +          sources += [
> +            "$root_gen_dir/mojo/public/tools/bindings/mojolpm_templates.zip",
> +          ]
> +        }
>          deps = [
>            ":$parser_target_name",
>            ":$type_mappings_target_name",
>            "//mojo/public/tools/bindings:precompile_templates",
>          ]
> +
>          if (defined(invoker.parser_deps)) {
>            deps += invoker.parser_deps
>          }
> @@ -1224,18 +1367,22 @@ template("mojom") {
>          args = common_generator_args + export_args
>          filelist = []
>          foreach(source, sources_list) {
> -          filelist += [ rebase_path("$source", root_build_dir) ]
> +          filelist += [ rebase_path(source, root_build_dir) ]
>          }
>          foreach(base_path, output_file_base_paths) {
> +          filename = get_path_info(base_path, "file")
> +          dirname = get_path_info(base_path, "dir")
> +          inputs += [ "$root_gen_dir/$dirname/${filename}-module" ]
> +
>            outputs += [
>              "$root_gen_dir/${base_path}${variant_dash_suffix}-forward.h",
>              "$root_gen_dir/${base_path}${variant_dash_suffix}-import-headers.h",
> -            "$root_gen_dir/${base_path}${variant_dash_suffix}-test-utils.cc",
>              "$root_gen_dir/${base_path}${variant_dash_suffix}-test-utils.h",
>              "$root_gen_dir/${base_path}${variant_dash_suffix}.cc",
>              "$root_gen_dir/${base_path}${variant_dash_suffix}.h",
>            ]
> -          if (generate_fuzzing && !defined(bindings_configuration.variant)) {
> +          if (generate_mojolpm_fuzzing &&
> +              !defined(bindings_configuration.variant)) {
>              outputs += [
>                "$root_gen_dir/${base_path}${variant_dash_suffix}-mojolpm.cc",
>                "$root_gen_dir/${base_path}${variant_dash_suffix}-mojolpm.h",
> @@ -1243,14 +1390,17 @@ template("mojom") {
>            }
>          }
>  
> -        response_file_contents = filelist
> -
> +        # Workaround for https://github.com/ninja-build/ninja/issues/1966.
> +        rsp_file = "$target_gen_dir/${target_name}.rsp"
> +        write_file(rsp_file, filelist)
> +        inputs += [ rsp_file ]
>          args += [
> -          "--filelist={{response_file_name}}",
> +          "--filelist=" + rebase_path("$rsp_file", root_build_dir),
>            "-g",
>          ]
>  
> -        if (generate_fuzzing && !defined(bindings_configuration.variant)) {
> +        if (generate_mojolpm_fuzzing &&
> +            !defined(bindings_configuration.variant)) {
>            args += [ "c++,mojolpm" ]
>          } else {
>            args += [ "c++" ]
> @@ -1294,6 +1444,8 @@ template("mojom") {
>                "--extra_cpp_template_paths",
>                rebase_path(extra_cpp_template, root_build_dir),
>              ]
> +            inputs += [ extra_cpp_template ]
> +
>              assert(
>                  get_path_info(extra_cpp_template, "extension") == "tmpl",
>                  "--extra_cpp_template_paths only accepts template files ending in extension .tmpl")
> @@ -1306,62 +1458,6 @@ template("mojom") {
>        }
>      }
>  
> -    if (generate_fuzzing && !defined(variant)) {
> -      # This block contains the C++ targets for the MojoLPM fuzzer, we need to
> -      # do this here so that we can use the typemap configuration for the
> -      # empty-variant Mojo target.
> -
> -      mojolpm_target_name = "${target_name}_mojolpm"
> -      mojolpm_generator_target_name = "${target_name}__generator"
> -      source_set(mojolpm_target_name) {
> -        # There are still a few missing header dependencies between mojo targets
> -        # with typemaps and the dependencies of their typemap headers. It would
> -        # be good to enable include checking for these in the future though.
> -        check_includes = false
> -        testonly = true
> -        if (defined(invoker.sources)) {
> -          sources = process_file_template(
> -                  invoker.sources,
> -                  [
> -                    "{{source_gen_dir}}/{{source_file_part}}-mojolpm.cc",
> -                    "{{source_gen_dir}}/{{source_file_part}}-mojolpm.h",
> -                  ])
> -          deps = []
> -        } else {
> -          sources = []
> -          deps = []
> -        }
> -
> -        public_deps = [
> -          ":$generator_shared_target_name",
> -
> -          # NB: hardcoded dependency on the no-variant variant generator, since
> -          # mojolpm only uses the no-variant type.
> -          ":$mojolpm_generator_target_name",
> -          ":$mojolpm_proto_target_name",
> -          "//base",
> -          "//mojo/public/tools/fuzzers:mojolpm",
> -        ]
> -
> -        foreach(d, all_deps) {
> -          # Resolve the name, so that a target //mojo/something becomes
> -          # //mojo/something:something and we can append variant_suffix to
> -          # get the cpp dependency name.
> -          full_name = get_label_info("$d", "label_no_toolchain")
> -          public_deps += [ "${full_name}_mojolpm" ]
> -        }
> -
> -        foreach(config, cpp_typemap_configs) {
> -          if (defined(config.traits_deps)) {
> -            deps += config.traits_deps
> -          }
> -          if (defined(config.traits_public_deps)) {
> -            public_deps += config.traits_public_deps
> -          }
> -        }
> -      }
> -    }
> -
>      # Write the typemapping configuration for this target out to a file to be
>      # validated by a Python script. This helps catch mistakes that can't
>      # be caught by logic in GN.
> @@ -1389,20 +1485,20 @@ template("mojom") {
>      write_file(_typemap_config_filename, _rebased_typemap_configs, "json")
>      _mojom_target_name = target_name
>  
> -    # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -    python2_action(_typemap_validator_target_name) {
> +    action(_typemap_validator_target_name) {
> +      allow_remote = true
>        script = "$mojom_generator_root/validate_typemap_config.py"
>        inputs = [ _typemap_config_filename ]
>        outputs = [ _typemap_stamp_filename ]
>        args = [
>          get_label_info(_mojom_target_name, "label_no_toolchain"),
> -        rebase_path(_typemap_config_filename),
> -        rebase_path(_typemap_stamp_filename),
> +        rebase_path(_typemap_config_filename, root_build_dir),
> +        rebase_path(_typemap_stamp_filename, root_build_dir),
>        ]
>      }
>  
> -    # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -    python2_action(type_mappings_target_name) {
> +    action(type_mappings_target_name) {
> +      allow_remote = true
>        inputs =
>            mojom_generator_sources + jinja2_sources + [ _typemap_stamp_filename ]
>        outputs = [ type_mappings_path ]
> @@ -1413,6 +1509,7 @@ template("mojom") {
>          rebase_path(type_mappings_path, root_build_dir),
>        ]
>  
> +      sources = []
>        foreach(d, all_deps) {
>          name = get_label_info(d, "label_no_toolchain")
>          toolchain = get_label_info(d, "toolchain")
> @@ -1422,12 +1519,11 @@ template("mojom") {
>          dependency_output_dir =
>              get_label_info(dependency_output, "target_gen_dir")
>          dependency_name = get_label_info(dependency_output, "name")
> -        dependency_path =
> -            rebase_path("$dependency_output_dir/${dependency_name}",
> -                        root_build_dir)
> +        dependency_path = "$dependency_output_dir/${dependency_name}"
> +        sources += [ dependency_path ]
>          args += [
>            "--dependency",
> -          dependency_path,
> +          rebase_path(dependency_path, root_build_dir),
>          ]
>        }
>  
> @@ -1485,11 +1581,15 @@ template("mojom") {
>        if (defined(output_name_override)) {
>          output_name = output_name_override
>        }
> -      visibility = output_visibility + [ ":$output_target_name" ]
> +      visibility = output_visibility + [
> +                     ":$output_target_name",
> +                     ":${target_name}_mojolpm",
> +                   ]
>        if (defined(invoker.testonly)) {
>          testonly = invoker.testonly
>        }
>        defines = export_defines
> +      configs += [ "//build/config/compiler:wexit_time_destructors" ]
>        configs += extra_configs
>        if (output_file_base_paths != []) {
>          sources = []
> @@ -1578,13 +1678,81 @@ template("mojom") {
>        }
>      }
>  
> +    if (generate_mojolpm_fuzzing && !defined(variant)) {
> +      # This block contains the C++ targets for the MojoLPM fuzzer, we need to
> +      # do this here so that we can use the typemap configuration for the
> +      # empty-variant Mojo target.
> +
> +      mojolpm_target_name = "${target_name}_mojolpm"
> +      mojolpm_generator_target_name = "${target_name}__generator"
> +      source_set(mojolpm_target_name) {
> +        # There are still a few missing header dependencies between mojo targets
> +        # with typemaps and the dependencies of their typemap headers. It would
> +        # be good to enable include checking for these in the future though.
> +        check_includes = false
> +        testonly = true
> +        if (defined(invoker.sources)) {
> +          # Split the input into generated and non-generated source files. They
> +          # need to be processed separately.
> +          gen_dir_path_wildcard = get_path_info("//", "gen_dir") + "/*"
> +          non_gen_sources =
> +              filter_exclude(invoker.sources, [ gen_dir_path_wildcard ])
> +          gen_sources =
> +              filter_include(invoker.sources, [ gen_dir_path_wildcard ])
> +          sources = process_file_template(
> +                  non_gen_sources,
> +                  [
> +                    "{{source_gen_dir}}/{{source_file_part}}-mojolpm.cc",
> +                    "{{source_gen_dir}}/{{source_file_part}}-mojolpm.h",
> +                  ])
> +          sources += process_file_template(
> +                  gen_sources,
> +                  [
> +                    "{{source_dir}}/{{source_file_part}}-mojolpm.cc",
> +                    "{{source_dir}}/{{source_file_part}}-mojolpm.h",
> +                  ])
> +          deps = [ ":$output_target_name" ]
> +        } else {
> +          sources = []
> +          deps = []
> +        }
> +
> +        public_deps = [
> +          ":$generator_shared_target_name",
> +
> +          # NB: hardcoded dependency on the no-variant variant generator, since
> +          # mojolpm only uses the no-variant type.
> +          ":$mojolpm_generator_target_name",
> +          ":$mojolpm_proto_target_name",
> +          "//base",
> +          "//mojo/public/tools/fuzzers:mojolpm",
> +        ]
> +
> +        foreach(d, all_deps) {
> +          # Resolve the name, so that a target //mojo/something becomes
> +          # //mojo/something:something and we can append variant_suffix to
> +          # get the cpp dependency name.
> +          full_name = get_label_info("$d", "label_no_toolchain")
> +          public_deps += [ "${full_name}_mojolpm" ]
> +        }
> +
> +        foreach(config, cpp_typemap_configs) {
> +          if (defined(config.traits_deps)) {
> +            deps += config.traits_deps
> +          }
> +          if (defined(config.traits_public_deps)) {
> +            public_deps += config.traits_public_deps
> +          }
> +        }
> +      }
> +    }
> +
>      if (generate_java && is_android) {
>        import("//build/config/android/rules.gni")
>  
>        java_generator_target_name = target_name + "_java__generator"
>        if (sources_list != []) {
> -        # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -        python2_action(java_generator_target_name) {
> +        action(java_generator_target_name) {
>            script = mojom_generator_script
>            inputs = mojom_generator_sources + jinja2_sources
>            sources = sources_list
> @@ -1597,7 +1765,7 @@ template("mojom") {
>            args = common_generator_args
>            filelist = []
>            foreach(source, sources_list) {
> -            filelist += [ rebase_path("$source", root_build_dir) ]
> +            filelist += [ rebase_path(source, root_build_dir) ]
>            }
>            foreach(base_path, output_file_base_paths) {
>              outputs += [ "$root_gen_dir/$base_path.srcjar" ]
> @@ -1624,8 +1792,7 @@ template("mojom") {
>  
>        java_srcjar_target_name = target_name + "_java_sources"
>  
> -      # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -      python2_action(java_srcjar_target_name) {
> +      action(java_srcjar_target_name) {
>          script = "//build/android/gyp/zip.py"
>          inputs = []
>          if (output_file_base_paths != []) {
> @@ -1651,7 +1818,6 @@ template("mojom") {
>        android_library(java_target_name) {
>          forward_variables_from(invoker, [ "enable_bytecode_checks" ])
>          deps = [
> -          "//base:base_java",
>            "//mojo/public/java:bindings_java",
>            "//mojo/public/java:system_java",
>            "//third_party/androidx:androidx_annotation_annotation_java",
> @@ -1673,21 +1839,36 @@ template("mojom") {
>      }
>    }
>  
> -  use_typescript_for_target =
> -      enable_typescript_bindings && defined(invoker.use_typescript_sources) &&
> -      invoker.use_typescript_sources
> -
> -  if (!use_typescript_for_target && defined(invoker.use_typescript_sources)) {
> -    not_needed(invoker, [ "use_typescript_sources" ])
> +  if (defined(invoker.generate_webui_js_bindings)) {
> +    assert(is_chromeos_ash,
> +           "generate_webui_js_bindings can only be used on ChromeOS Ash")
> +    assert(invoker.generate_webui_js_bindings,
> +           "generate_webui_js_bindings should be set to true or removed")
>    }
>  
> -  if ((generate_fuzzing || !defined(invoker.cpp_only) || !invoker.cpp_only) &&
> -      !use_typescript_for_target) {
> +  use_typescript_for_target = defined(invoker.webui_module_path) &&
> +                              !defined(invoker.generate_webui_js_bindings)
> +
> +  generate_legacy_js = !use_typescript_for_target ||
> +                       (defined(invoker.generate_legacy_js_bindings) &&
> +                        invoker.generate_legacy_js_bindings)
> +
> +  if (!use_typescript_for_target &&
> +      defined(invoker.generate_legacy_js_bindings)) {
> +    not_needed(invoker, [ "generate_legacy_js_bindings" ])
> +  }
> +
> +  # Targets needed by both TS and JS bindings targets. These are needed
> +  # unconditionally for JS bindings targets, and are needed for TS bindings
> +  # targets when generate_legacy_js_bindings is true. This option is provided
> +  # since the legacy bindings are needed by Blink tests and non-Chromium users,
> +  # which are not expected to migrate to modules or TypeScript.
> +  if (generate_legacy_js && (generate_js_fuzzing ||
> +                             !defined(invoker.cpp_only) || !invoker.cpp_only)) {
>      if (sources_list != []) {
>        generator_js_target_name = "${target_name}_js__generator"
>  
> -      # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -      python2_action(generator_js_target_name) {
> +      action(generator_js_target_name) {
>          script = mojom_generator_script
>          inputs = mojom_generator_sources + jinja2_sources
>          sources = sources_list
> @@ -1702,19 +1883,18 @@ template("mojom") {
>          args = common_generator_args
>          filelist = []
>          foreach(source, sources_list) {
> -          filelist += [ rebase_path("$source", root_build_dir) ]
> +          filelist += [ rebase_path(source, root_build_dir) ]
>          }
>          foreach(base_path, output_file_base_paths) {
>            outputs += [
>              "$root_gen_dir/$base_path.js",
> -            "$root_gen_dir/$base_path.externs.js",
>              "$root_gen_dir/$base_path.m.js",
>              "$root_gen_dir/$base_path-lite.js",
> -            "$root_gen_dir/$base_path.html",
>              "$root_gen_dir/$base_path-lite-for-compile.js",
>            ]
>  
> -          if (defined(invoker.webui_module_path)) {
> +          if (defined(invoker.webui_module_path) &&
> +              !use_typescript_for_target) {
>              outputs += [ "$root_gen_dir/mojom-webui/$base_path-webui.js" ]
>            }
>          }
> @@ -1725,7 +1905,6 @@ template("mojom") {
>            "--filelist={{response_file_name}}",
>            "-g",
>            "javascript",
> -          "--js_bindings_mode=new",
>          ]
>  
>          if (defined(invoker.js_generate_struct_deserializers) &&
> @@ -1739,7 +1918,7 @@ template("mojom") {
>            args += message_scrambling_args
>          }
>  
> -        if (generate_fuzzing) {
> +        if (generate_js_fuzzing) {
>            args += [ "--generate_fuzzing" ]
>          }
>        }
> @@ -1783,31 +1962,13 @@ template("mojom") {
>          data_deps += [ "${full_name}_js_data_deps" ]
>        }
>      }
> +  }
>  
> -    js_library_target_name = "${target_name}_js_library"
> -    if (sources_list != []) {
> -      js_library(js_library_target_name) {
> -        extra_public_deps = [ ":$generator_js_target_name" ]
> -        sources = []
> -        foreach(base_path, output_file_base_paths) {
> -          sources += [ "$root_gen_dir/${base_path}-lite.js" ]
> -        }
> -        externs_list = [
> -          "${externs_path}/mojo_core.js",
> -          "${externs_path}/pending.js",
> -        ]
> -
> -        deps = []
> -        foreach(d, all_deps) {
> -          full_name = get_label_info(d, "label_no_toolchain")
> -          deps += [ "${full_name}_js_library" ]
> -        }
> -      }
> -    } else {
> -      group(js_library_target_name) {
> -      }
> -    }
> -
> +  # js_library() closure compiler targets, primarily used on ChromeOS. Only
> +  # generate these targets if the mojom target is not C++ only and is not using
> +  # TypeScript.
> +  if (generate_mojom_closure_libraries &&
> +      (!defined(invoker.cpp_only) || !invoker.cpp_only) && generate_legacy_js) {
>      js_library_for_compile_target_name = "${target_name}_js_library_for_compile"
>      if (sources_list != []) {
>        js_library(js_library_for_compile_target_name) {
> @@ -1834,35 +1995,9 @@ template("mojom") {
>        }
>      }
>  
> -    js_modules_target_name = "${target_name}_js_modules"
> -    if (sources_list != []) {
> -      js_library(js_modules_target_name) {
> -        extra_public_deps = [ ":$generator_js_target_name" ]
> -        sources = []
> -        foreach(base_path, output_file_base_paths) {
> -          sources += [ "$root_gen_dir/${base_path}.m.js" ]
> -        }
> -        externs_list = [
> -          "${externs_path}/mojo_core.js",
> -          "${externs_path}/pending.js",
> -        ]
> -        if (defined(invoker.disallow_native_types) &&
> -            invoker.disallow_native_types) {
> -          deps = []
> -        } else {
> -          deps = [ "//mojo/public/js:bindings_uncompiled" ]
> -        }
> -        foreach(d, all_deps) {
> -          full_name = get_label_info(d, "label_no_toolchain")
> -          deps += [ "${full_name}_js_modules" ]
> -        }
> -      }
> -    } else {
> -      group(js_modules_target_name) {
> -      }
> -    }
> -
> -    if (defined(invoker.webui_module_path)) {
> +    # WebUI specific closure targets, not needed by targets that are generating
> +    # TypeScript WebUI bindings or by legacy-only targets.
> +    if (defined(invoker.webui_module_path) && !use_typescript_for_target) {
>        webui_js_target_name = "${target_name}_webui_js"
>        if (sources_list != []) {
>          js_library(webui_js_target_name) {
> @@ -1890,46 +2025,38 @@ template("mojom") {
>          group(webui_js_target_name) {
>          }
>        }
> +
> +      webui_grdp_target_name = "${target_name}_webui_grdp"
> +      out_grd = "$target_gen_dir/${target_name}_webui_resources.grdp"
> +      grd_prefix = "${target_name}_webui"
> +      generate_grd(webui_grdp_target_name) {
> +        grd_prefix = grd_prefix
> +        out_grd = out_grd
> +
> +        deps = [ ":$webui_js_target_name" ]
> +
> +        input_files = []
> +        foreach(base_path, output_file_base_paths) {
> +          input_files += [ "${base_path}-webui.js" ]
> +        }
> +
> +        input_files_base_dir =
> +            rebase_path("$root_gen_dir/mojom-webui", "$root_build_dir")
> +      }
>      }
>    }
> -  if ((generate_fuzzing || !defined(invoker.cpp_only) || !invoker.cpp_only) &&
> -      use_typescript_for_target) {
> -    generator_js_target_names = []
> -    source_filelist = []
> -    foreach(source, sources_list) {
> -      source_filelist += [ rebase_path("$source", root_build_dir) ]
> -    }
> -
> -    dependency_types = [
> -      {
> -        name = "regular"
> -        ts_extension = ".ts"
> -        js_extension = ".js"
> -      },
> -      {
> -        name = "es_modules"
> -        ts_extension = ".m.ts"
> -        js_extension = ".m.js"
> -      },
> -    ]
> -
> -    foreach(dependency_type, dependency_types) {
> -      ts_outputs = []
> -      js_outputs = []
> -
> -      foreach(base_path, output_file_base_paths) {
> -        ts_outputs +=
> -            [ "$root_gen_dir/$base_path-lite${dependency_type.ts_extension}" ]
> -        js_outputs +=
> -            [ "$root_gen_dir/$base_path-lite${dependency_type.js_extension}" ]
> +  if ((generate_js_fuzzing || !defined(invoker.cpp_only) ||
> +       !invoker.cpp_only) && use_typescript_for_target) {
> +    if (sources_list != []) {
> +      source_filelist = []
> +      foreach(source, sources_list) {
> +        source_filelist += [ rebase_path(source, root_build_dir) ]
>        }
>  
>        # Generate Typescript bindings.
> -      generator_ts_target_name =
> -          "${target_name}_${dependency_type.name}__ts__generator"
> +      generator_ts_target_name = "${target_name}_ts__generator"
>  
> -      # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -      python2_action(generator_ts_target_name) {
> +      action(generator_ts_target_name) {
>          script = mojom_generator_script
>          inputs = mojom_generator_sources + jinja2_sources
>          sources = sources_list
> @@ -1938,7 +2065,10 @@ template("mojom") {
>            "//mojo/public/tools/bindings:precompile_templates",
>          ]
>  
> -        outputs = ts_outputs
> +        outputs = []
> +        foreach(base_path, output_file_base_paths) {
> +          outputs += [ "$root_gen_dir/$base_path-webui.ts" ]
> +        }
>          args = common_generator_args
>          response_file_contents = source_filelist
>  
> @@ -1948,98 +2078,21 @@ template("mojom") {
>            "typescript",
>          ]
>  
> -        if (dependency_type.name == "es_modules") {
> -          args += [ "--ts_use_es_modules" ]
> +        if (!defined(invoker.scramble_message_ids) ||
> +            invoker.scramble_message_ids) {
> +          inputs += message_scrambling_inputs
> +          args += message_scrambling_args
>          }
>  
> -        # TODO(crbug.com/1007587): Support scramble_message_ids.
> +        if (defined(invoker.js_generate_struct_deserializers) &&
> +            invoker.js_generate_struct_deserializers) {
> +          args += [ "--js_generate_struct_deserializers" ]
> +        }
> +
> +        # TODO(crbug.com/1007587): Support scramble_message_ids if above is
> +        # insufficient.
>          # TODO(crbug.com/1007591): Support generate_fuzzing.
>        }
> -
> -      # Create tsconfig.json for the generated Typescript.
> -      tsconfig_filename =
> -          "$target_gen_dir/$target_name-${dependency_type.name}-tsconfig.json"
> -      tsconfig = {
> -      }
> -      tsconfig.compilerOptions = {
> -        composite = true
> -        target = "es6"
> -        module = "es6"
> -        lib = [
> -          "es6",
> -          "esnext.bigint",
> -        ]
> -        strict = true
> -      }
> -      tsconfig.files = []
> -      foreach(base_path, output_file_base_paths) {
> -        tsconfig.files += [ rebase_path(
> -                "$root_gen_dir/$base_path-lite${dependency_type.ts_extension}",
> -                target_gen_dir,
> -                root_gen_dir) ]
> -      }
> -      tsconfig.references = []
> -
> -      # Get tsconfigs for deps.
> -      foreach(d, all_deps) {
> -        dep_target_gen_dir = rebase_path(get_label_info(d, "target_gen_dir"))
> -        dep_name = get_label_info(d, "name")
> -        reference = {
> -        }
> -        reference.path = "$dep_target_gen_dir/$dep_name-${dependency_type.name}-tsconfig.json"
> -        tsconfig.references += [ reference ]
> -      }
> -      write_file(tsconfig_filename, tsconfig, "json")
> -
> -      # Compile previously generated Typescript to Javascript.
> -      generator_js_target_name =
> -          "${target_name}_${dependency_type.name}__js__generator"
> -      generator_js_target_names += [ generator_js_target_name ]
> -
> -      # TODO(crbug.com/1194274): Investigate nondeterminism in Py3 builds.
> -      python2_action(generator_js_target_name) {
> -        script = "$mojom_generator_root/compile_typescript.py"
> -        sources = ts_outputs
> -        outputs = js_outputs
> -        public_deps = [ ":$generator_ts_target_name" ]
> -        foreach(d, all_deps) {
> -          full_name = get_label_info(d, "label_no_toolchain")
> -          public_deps +=
> -              [ "${full_name}_${dependency_type.name}__js__generator" ]
> -        }
> -
> -        absolute_tsconfig_path =
> -            rebase_path(tsconfig_filename, "", target_gen_dir)
> -        args = [ "--tsconfig_path=$absolute_tsconfig_path" ]
> -      }
> -    }
> -
> -    js_target_name = target_name + "_js"
> -    group(js_target_name) {
> -      public_deps = []
> -      if (sources_list != []) {
> -        foreach(generator_js_target_name, generator_js_target_names) {
> -          public_deps += [ ":$generator_js_target_name" ]
> -        }
> -      }
> -
> -      foreach(d, all_deps) {
> -        full_name = get_label_info(d, "label_no_toolchain")
> -        public_deps += [ "${full_name}_js" ]
> -      }
> -    }
> -
> -    group(js_data_deps_target_name) {
> -      data = js_outputs
> -      deps = []
> -      foreach(generator_js_target_name, generator_js_target_names) {
> -        deps += [ ":$generator_js_target_name" ]
> -      }
> -      data_deps = []
> -      foreach(d, all_deps) {
> -        full_name = get_label_info(d, "label_no_toolchain")
> -        data_deps += [ "${full_name}_js_data_deps" ]
> -      }
>      }
>    }
>  }
> diff --git a/utils/ipc/mojo/public/tools/bindings/mojom_bindings_generator.py b/utils/ipc/mojo/public/tools/bindings/mojom_bindings_generator.py
> index da9efc71cefd..8c641c2aa8a6 100755
> --- a/utils/ipc/mojo/public/tools/bindings/mojom_bindings_generator.py
> +++ b/utils/ipc/mojo/public/tools/bindings/mojom_bindings_generator.py
> @@ -1,5 +1,5 @@
>  #!/usr/bin/env python
> -# Copyright 2013 The Chromium Authors. All rights reserved.
> +# Copyright 2013 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -57,10 +57,17 @@ _BUILTIN_GENERATORS = {
>      "typescript": "mojom_ts_generator",
>  }
>  
> +_BUILTIN_CHECKS = {
> +    "attributes": "mojom_attributes_check",
> +    "definitions": "mojom_definitions_check",
> +    "features": "mojom_interface_feature_check",
> +    "restrictions": "mojom_restrictions_check",
> +}
> +
>  
>  def LoadGenerators(generators_string):
>    if not generators_string:
> -    return []  # No generators.
> +    return {}  # No generators.
>  
>    generators = {}
>    for generator_name in [s.strip() for s in generators_string.split(",")]:
> @@ -74,6 +81,21 @@ def LoadGenerators(generators_string):
>    return generators
>  
>  
> +def LoadChecks(checks_string):
> +  if not checks_string:
> +    return {}  # No checks.
> +
> +  checks = {}
> +  for check_name in [s.strip() for s in checks_string.split(",")]:
> +    check = check_name.lower()
> +    if check not in _BUILTIN_CHECKS:
> +      print("Unknown check name %s" % check_name)
> +      sys.exit(1)
> +    check_module = importlib.import_module("checks.%s" % _BUILTIN_CHECKS[check])
> +    checks[check] = check_module
> +  return checks
> +
> +
>  def MakeImportStackMessage(imported_filename_stack):
>    """Make a (human-readable) message listing a chain of imports. (Returned
>    string begins with a newline (if nonempty) and does not end with one.)"""
> @@ -82,7 +104,7 @@ def MakeImportStackMessage(imported_filename_stack):
>                      zip(imported_filename_stack[1:], imported_filename_stack)]))
>  
>  
> -class RelativePath(object):
> +class RelativePath:
>    """Represents a path relative to the source tree or generated output dir."""
>  
>    def __init__(self, path, source_root, output_dir):
> @@ -142,7 +164,7 @@ def ReadFileContents(filename):
>      return f.read()
>  
>  
> -class MojomProcessor(object):
> +class MojomProcessor:
>    """Takes parsed mojom modules and generates language bindings from them.
>  
>    Attributes:
> @@ -169,8 +191,8 @@ class MojomProcessor(object):
>      if 'c++' in self._typemap:
>        self._typemap['mojolpm'] = self._typemap['c++']
>  
> -  def _GenerateModule(self, args, remaining_args, generator_modules,
> -                      rel_filename, imported_filename_stack):
> +  def _GenerateModule(self, args, remaining_args, check_modules,
> +                      generator_modules, rel_filename, imported_filename_stack):
>      # Return the already-generated module.
>      if rel_filename.path in self._processed_files:
>        return self._processed_files[rel_filename.path]
> @@ -190,12 +212,16 @@ class MojomProcessor(object):
>        ScrambleMethodOrdinals(module.interfaces, salt)
>  
>      if self._should_generate(rel_filename.path):
> +      # Run checks on module first.
> +      for check_module in check_modules.values():
> +        checker = check_module.Check(module)
> +        checker.CheckModule()
> +      # Then run generation.
>        for language, generator_module in generator_modules.items():
>          generator = generator_module.Generator(
>              module, args.output_dir, typemap=self._typemap.get(language, {}),
>              variant=args.variant, bytecode_path=args.bytecode_path,
>              for_blink=args.for_blink,
> -            js_bindings_mode=args.js_bindings_mode,
>              js_generate_struct_deserializers=\
>                      args.js_generate_struct_deserializers,
>              export_attribute=args.export_attribute,
> @@ -234,6 +260,7 @@ def _Generate(args, remaining_args):
>        args.import_directories[idx] = RelativePath(tokens[0], args.depth,
>                                                    args.output_dir)
>    generator_modules = LoadGenerators(args.generators_string)
> +  check_modules = LoadChecks(args.checks_string)
>  
>    fileutil.EnsureDirectoryExists(args.output_dir)
>  
> @@ -246,7 +273,7 @@ def _Generate(args, remaining_args):
>  
>    for filename in args.filename:
>      processor._GenerateModule(
> -        args, remaining_args, generator_modules,
> +        args, remaining_args, check_modules, generator_modules,
>          RelativePath(filename, args.depth, args.output_dir), [])
>  
>    return 0
> @@ -286,6 +313,12 @@ def main():
>                                 metavar="GENERATORS",
>                                 default="c++,javascript,java,mojolpm",
>                                 help="comma-separated list of generators")
> +  generate_parser.add_argument("-c",
> +                               "--checks",
> +                               dest="checks_string",
> +                               metavar="CHECKS",
> +                               default=",".join(_BUILTIN_CHECKS.keys()),
> +                               help="comma-separated list of checks")
>    generate_parser.add_argument(
>        "--gen_dir", dest="gen_directories", action="append", metavar="directory",
>        default=[], help="add a directory to be searched for the syntax trees.")
> @@ -308,11 +341,6 @@ def main():
>    generate_parser.add_argument("--for_blink", action="store_true",
>                                 help="Use WTF types as generated types for mojo "
>                                 "string/array/map.")
> -  generate_parser.add_argument(
> -      "--js_bindings_mode", choices=["new", "old"], default="old",
> -      help="This option only affects the JavaScript bindings. The value could "
> -      "be \"new\" to generate new-style lite JS bindings in addition to the "
> -      "old, or \"old\" to only generate old bindings.")
>    generate_parser.add_argument(
>        "--js_generate_struct_deserializers", action="store_true",
>        help="Generate javascript deserialize methods for structs in "
> @@ -387,4 +415,10 @@ def main():
>  
>  if __name__ == "__main__":
>    with crbug_1001171.DumpStateOnLookupError():
> -    sys.exit(main())
> +    ret = main()
> +    # Exit without running GC, which can save multiple seconds due to the large
> +    # number of object created. But flush is necessary as os._exit doesn't do
> +    # that.
> +    sys.stdout.flush()
> +    sys.stderr.flush()
> +    os._exit(ret)
> diff --git a/utils/ipc/mojo/public/tools/bindings/mojom_bindings_generator_unittest.py b/utils/ipc/mojo/public/tools/bindings/mojom_bindings_generator_unittest.py
> index bddbe3f4c580..761922b6777e 100644
> --- a/utils/ipc/mojo/public/tools/bindings/mojom_bindings_generator_unittest.py
> +++ b/utils/ipc/mojo/public/tools/bindings/mojom_bindings_generator_unittest.py
> @@ -1,4 +1,4 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -8,13 +8,13 @@ from mojom_bindings_generator import MakeImportStackMessage
>  from mojom_bindings_generator import ScrambleMethodOrdinals
>  
>  
> -class FakeIface(object):
> +class FakeIface:
>    def __init__(self):
>      self.mojom_name = None
>      self.methods = None
>  
>  
> -class FakeMethod(object):
> +class FakeMethod:
>    def __init__(self, explicit_ordinal=None):
>      self.explicit_ordinal = explicit_ordinal
>      self.ordinal = explicit_ordinal
> diff --git a/utils/ipc/mojo/public/tools/bindings/mojom_types_downgrader.py b/utils/ipc/mojo/public/tools/bindings/mojom_types_downgrader.py
> deleted file mode 100755
> index 15f0e3bac1f7..000000000000
> --- a/utils/ipc/mojo/public/tools/bindings/mojom_types_downgrader.py
> +++ /dev/null
> @@ -1,119 +0,0 @@
> -#!/usr/bin/env python
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> -# Use of this source code is governed by a BSD-style license that can be
> -# found in the LICENSE file.
> -"""Downgrades *.mojom files to the old mojo types for remotes and receivers."""
> -
> -import argparse
> -import fnmatch
> -import os
> -import re
> -import shutil
> -import sys
> -import tempfile
> -
> -# List of patterns and replacements to match and use against the contents of a
> -# mojo file. Each replacement string will be used with Python string's format()
> -# function, so the '{}' substring is used to mark where the mojo type should go.
> -_MOJO_REPLACEMENTS = {
> -    r'pending_remote': r'{}',
> -    r'pending_receiver': r'{}&',
> -    r'pending_associated_remote': r'associated {}',
> -    r'pending_associated_receiver': r'associated {}&',
> -}
> -
> -# Pre-compiled regular expression that matches against any of the replacements.
> -_REGEXP_PATTERN = re.compile(
> -    r'|'.join(
> -        ['{}\s*<\s*(.*?)\s*>'.format(k) for k in _MOJO_REPLACEMENTS.keys()]),
> -    flags=re.DOTALL)
> -
> -
> -def ReplaceFunction(match_object):
> -  """Returns the right replacement for the string matched against the regexp."""
> -  for index, (match, repl) in enumerate(_MOJO_REPLACEMENTS.items(), 1):
> -    if match_object.group(0).startswith(match):
> -      return repl.format(match_object.group(index))
> -
> -
> -def DowngradeFile(path, output_dir=None):
> -  """Downgrades the mojom file specified by |path| to the old mojo types.
> -
> -  Optionally pass |output_dir| to place the result under a separate output
> -  directory, preserving the relative path to the file included in |path|.
> -  """
> -  # Use a temporary file to dump the new contents after replacing the patterns.
> -  with open(path) as src_mojo_file:
> -    with tempfile.NamedTemporaryFile(mode='w', delete=False) as tmp_mojo_file:
> -      tmp_contents = _REGEXP_PATTERN.sub(ReplaceFunction, src_mojo_file.read())
> -      tmp_mojo_file.write(tmp_contents)
> -
> -  # Files should be placed in the desired output directory
> -  if output_dir:
> -    output_filepath = os.path.join(output_dir, os.path.basename(path))
> -    if not os.path.exists(output_dir):
> -      os.makedirs(output_dir)
> -  else:
> -    output_filepath = path
> -
> -  # Write the new contents preserving the original file's attributes.
> -  shutil.copystat(path, tmp_mojo_file.name)
> -  shutil.move(tmp_mojo_file.name, output_filepath)
> -
> -  # Make sure to "touch" the new file so that access, modify and change times
> -  # are always newer than the source file's, otherwise Modify time will be kept
> -  # as per the call to shutil.copystat(), causing unnecessary generations of the
> -  # output file in subsequent builds due to ninja considering it dirty.
> -  os.utime(output_filepath, None)
> -
> -
> -def DowngradeDirectory(path, output_dir=None):
> -  """Downgrades mojom files inside directory |path| to the old mojo types.
> -
> -  Optionally pass |output_dir| to place the result under a separate output
> -  directory, preserving the relative path to the file included in |path|.
> -  """
> -  # We don't have recursive glob.glob() nor pathlib.Path.rglob() in Python 2.7
> -  mojom_filepaths = []
> -  for dir_path, _, filenames in os.walk(path):
> -    for filename in fnmatch.filter(filenames, "*mojom"):
> -      mojom_filepaths.append(os.path.join(dir_path, filename))
> -
> -  for path in mojom_filepaths:
> -    absolute_dirpath = os.path.dirname(os.path.abspath(path))
> -    if output_dir:
> -      dest_dirpath = output_dir + absolute_dirpath
> -    else:
> -      dest_dirpath = absolute_dirpath
> -    DowngradeFile(path, dest_dirpath)
> -
> -
> -def DowngradePath(src_path, output_dir=None):
> -  """Downgrades the mojom files pointed by |src_path| to the old mojo types.
> -
> -  Optionally pass |output_dir| to place the result under a separate output
> -  directory, preserving the relative path to the file included in |path|.
> -  """
> -  if os.path.isdir(src_path):
> -    DowngradeDirectory(src_path, output_dir)
> -  elif os.path.isfile(src_path):
> -    DowngradeFile(src_path, output_dir)
> -  else:
> -    print(">>> {} not pointing to a valid file or directory".format(src_path))
> -    sys.exit(1)
> -
> -
> -def main():
> -  parser = argparse.ArgumentParser(
> -      description="Downgrade *.mojom files to use the old mojo types.")
> -  parser.add_argument(
> -      "srcpath", help="path to the file or directory to apply the conversion")
> -  parser.add_argument(
> -      "--outdir", help="the directory to place the converted file(s) under")
> -  args = parser.parse_args()
> -
> -  DowngradePath(args.srcpath, args.outdir)
> -
> -
> -if __name__ == "__main__":
> -  sys.exit(main())
> diff --git a/utils/ipc/mojo/public/tools/bindings/validate_typemap_config.py b/utils/ipc/mojo/public/tools/bindings/validate_typemap_config.py
> index f1783d59b951..6bb7a209310e 100755
> --- a/utils/ipc/mojo/public/tools/bindings/validate_typemap_config.py
> +++ b/utils/ipc/mojo/public/tools/bindings/validate_typemap_config.py
> @@ -1,5 +1,5 @@
>  #!/usr/bin/env python
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -17,7 +17,8 @@ def CheckCppTypemapConfigs(target_name, config_filename, out_filename):
>    ])
>    _SUPPORTED_TYPE_KEYS = set([
>        'mojom', 'cpp', 'copyable_pass_by_value', 'force_serialize', 'hashable',
> -      'move_only', 'nullable_is_same_type'
> +      'move_only', 'nullable_is_same_type', 'forward_declaration',
> +      'default_constructible'
>    ])
>    with open(config_filename, 'r') as f:
>      for config in json.load(f):
> diff --git a/utils/ipc/mojo/public/tools/mojom/BUILD.gn b/utils/ipc/mojo/public/tools/mojom/BUILD.gn
> new file mode 100644
> index 000000000000..eafb95a18ad1
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/mojom/BUILD.gn
> @@ -0,0 +1,18 @@
> +# Copyright 2022 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +
> +group("tests") {
> +  data = [
> +    "check_stable_mojom_compatibility_unittest.py",
> +    "check_stable_mojom_compatibility.py",
> +    "const_unittest.py",
> +    "enum_unittest.py",
> +    "feature_unittest.py",
> +    "mojom_parser_test_case.py",
> +    "mojom_parser_unittest.py",
> +    "mojom_parser.py",
> +    "stable_attribute_unittest.py",
> +    "version_compatibility_unittest.py",
> +  ]
> +}
> diff --git a/utils/ipc/mojo/public/tools/mojom/check_stable_mojom_compatibility.py b/utils/ipc/mojo/public/tools/mojom/check_stable_mojom_compatibility.py
> index 08bd672f5ba5..35cd1cfde155 100755
> --- a/utils/ipc/mojo/public/tools/mojom/check_stable_mojom_compatibility.py
> +++ b/utils/ipc/mojo/public/tools/mojom/check_stable_mojom_compatibility.py
> @@ -1,5 +1,5 @@
> -#!/usr/bin/env python
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +#!/usr/bin/env python3
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Verifies backward-compatibility of mojom type changes.
> @@ -12,20 +12,18 @@ This can be used e.g. by a presubmit check to prevent developers from making
>  breaking changes to stable mojoms."""
>  
>  import argparse
> -import errno
>  import io
>  import json
>  import os
>  import os.path
> -import shutil
> -import six
>  import sys
> -import tempfile
>  
>  from mojom.generate import module
>  from mojom.generate import translate
>  from mojom.parse import parser
>  
> +# pylint: disable=raise-missing-from
> +
>  
>  class ParseError(Exception):
>    pass
> @@ -41,6 +39,8 @@ def _ValidateDelta(root, delta):
>    transitive closure of a mojom's input dependencies all at once.
>    """
>  
> +  translate.is_running_backwards_compatibility_check_hack = True
> +
>    # First build a map of all files covered by the delta
>    affected_files = set()
>    old_files = {}
> @@ -73,11 +73,35 @@ def _ValidateDelta(root, delta):
>      try:
>        ast = parser.Parse(contents, mojom)
>      except Exception as e:
> -      six.reraise(
> -          ParseError,
> -          'encountered exception {0} while parsing {1}'.format(e, mojom),
> -          sys.exc_info()[2])
> +      raise ParseError('encountered exception {0} while parsing {1}'.format(
> +          e, mojom))
> +
> +    # Files which are generated at compile time can't be checked by this script
> +    # (at the moment) since they may not exist in the output directory.
> +    generated_files_to_skip = {
> +        ('third_party/blink/public/mojom/runtime_feature_state/'
> +         'runtime_feature.mojom'),
> +        ('third_party/blink/public/mojom/origin_trial_feature/'
> +         'origin_trial_feature.mojom'),
> +    }
> +
> +    ast.import_list.items = [
> +        x for x in ast.import_list.items
> +        if x.import_filename not in generated_files_to_skip
> +    ]
> +
>      for imp in ast.import_list:
> +      if (not file_overrides.get(imp.import_filename)
> +          and not os.path.exists(os.path.join(root, imp.import_filename))):
> +        # Speculatively construct a path prefix to locate the import_filename
> +        mojom_path = os.path.dirname(os.path.normpath(mojom)).split(os.sep)
> +        test_prefix = ''
> +        for path_component in mojom_path:
> +          test_prefix = os.path.join(test_prefix, path_component)
> +          test_import_filename = os.path.join(test_prefix, imp.import_filename)
> +          if os.path.exists(os.path.join(root, test_import_filename)):
> +            imp.import_filename = test_import_filename
> +            break
>        parseMojom(imp.import_filename, file_overrides, override_modules)
>  
>      # Now that the transitive set of dependencies has been imported and parsed
> @@ -89,10 +113,10 @@ def _ValidateDelta(root, delta):
>      modules[mojom] = translate.OrderedModule(ast, mojom, all_modules)
>  
>    old_modules = {}
> -  for mojom in old_files.keys():
> +  for mojom in old_files:
>      parseMojom(mojom, old_files, old_modules)
>    new_modules = {}
> -  for mojom in new_files.keys():
> +  for mojom in new_files:
>      parseMojom(mojom, new_files, new_modules)
>  
>    # At this point we have a complete set of translated Modules from both the
> @@ -132,12 +156,21 @@ def _ValidateDelta(root, delta):
>            'can be deleted by a subsequent change.' % qualified_name)
>  
>      checker = module.BackwardCompatibilityChecker()
> -    if not checker.IsBackwardCompatible(new_types[new_name], kind):
> -      raise Exception('Stable type %s appears to have changed in a way which '
> -                      'breaks backward-compatibility. Please fix!\n\nIf you '
> -                      'believe this assessment to be incorrect, please file a '
> -                      'Chromium bug against the "Internals>Mojo>Bindings" '
> -                      'component.' % qualified_name)
> +    try:
> +      if not checker.IsBackwardCompatible(new_types[new_name], kind):
> +        raise Exception(
> +            'Stable type %s appears to have changed in a way which '
> +            'breaks backward-compatibility. Please fix!\n\nIf you '
> +            'believe this assessment to be incorrect, please file a '
> +            'Chromium bug against the "Internals>Mojo>Bindings" '
> +            'component.' % qualified_name)
> +    except Exception as e:
> +      raise Exception(
> +          'Stable type %s appears to have changed in a way which '
> +          'breaks backward-compatibility: \n\n%s.\nPlease fix!\n\nIf you '
> +          'believe this assessment to be incorrect, please file a '
> +          'Chromium bug against the "Internals>Mojo>Bindings" '
> +          'component.' % (qualified_name, e))
>  
>  
>  def Run(command_line, delta=None):
> diff --git a/utils/ipc/mojo/public/tools/mojom/check_stable_mojom_compatibility_unittest.py b/utils/ipc/mojo/public/tools/mojom/check_stable_mojom_compatibility_unittest.py
> index 9f51ea7751fb..06769c9533c3 100755
> --- a/utils/ipc/mojo/public/tools/mojom/check_stable_mojom_compatibility_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/check_stable_mojom_compatibility_unittest.py
> @@ -1,5 +1,5 @@
> -#!/usr/bin/env python
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +#!/usr/bin/env python3
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -15,7 +15,7 @@ import check_stable_mojom_compatibility
>  from mojom.generate import module
>  
>  
> -class Change(object):
> +class Change:
>    """Helper to clearly define a mojom file delta to be analyzed."""
>  
>    def __init__(self, filename, old=None, new=None):
> @@ -28,7 +28,7 @@ class Change(object):
>  
>  class UnchangedFile(Change):
>    def __init__(self, filename, contents):
> -    super(UnchangedFile, self).__init__(filename, old=contents, new=contents)
> +    super().__init__(filename, old=contents, new=contents)
>  
>  
>  class CheckStableMojomCompatibilityTest(unittest.TestCase):
> @@ -258,3 +258,82 @@ class CheckStableMojomCompatibilityTest(unittest.TestCase):
>                 [Stable] struct T { foo.S s; int32 x; };
>                 """)
>      ])
> +
> +  def testWithPartialImport(self):
> +    """The compatibility checking tool correctly parses imports with partial
> +    paths."""
> +    self.assertBackwardCompatible([
> +        UnchangedFile('foo/foo.mojom', 'module foo; [Stable] struct S {};'),
> +        Change('foo/bar.mojom',
> +               old="""\
> +               module bar;
> +               import "foo/foo.mojom";
> +               [Stable] struct T { foo.S s; };
> +               """,
> +               new="""\
> +               module bar;
> +               import "foo.mojom";
> +               [Stable] struct T { foo.S s; };
> +               """)
> +    ])
> +
> +    self.assertBackwardCompatible([
> +        UnchangedFile('foo/foo.mojom', 'module foo; [Stable] struct S {};'),
> +        Change('foo/bar.mojom',
> +               old="""\
> +               module bar;
> +               import "foo.mojom";
> +               [Stable] struct T { foo.S s; };
> +               """,
> +               new="""\
> +               module bar;
> +               import "foo/foo.mojom";
> +               [Stable] struct T { foo.S s; };
> +               """)
> +    ])
> +
> +    self.assertNotBackwardCompatible([
> +        UnchangedFile('foo/foo.mojom', 'module foo; [Stable] struct S {};'),
> +        Change('bar/bar.mojom',
> +               old="""\
> +               module bar;
> +               import "foo/foo.mojom";
> +               [Stable] struct T { foo.S s; };
> +               """,
> +               new="""\
> +               module bar;
> +               import "foo.mojom";
> +               [Stable] struct T { foo.S s; };
> +               """)
> +    ])
> +
> +    self.assertNotBackwardCompatible([
> +        UnchangedFile('foo/foo.mojom', 'module foo; [Stable] struct S {};'),
> +        Change('bar/bar.mojom',
> +               old="""\
> +               module bar;
> +               import "foo.mojom";
> +               [Stable] struct T { foo.S s; };
> +               """,
> +               new="""\
> +               module bar;
> +               import "foo/foo.mojom";
> +               [Stable] struct T { foo.S s; };
> +               """)
> +    ])
> +
> +  def testNewEnumDefault(self):
> +    # Should be backwards compatible since it does not affect the wire format.
> +    # This specific case also checks that the backwards compatibility checker
> +    # does not throw an error due to the older version of the enum not
> +    # specifying [Default].
> +    self.assertBackwardCompatible([
> +        Change('foo/foo.mojom',
> +               old='[Extensible] enum E { One };',
> +               new='[Extensible] enum E { [Default] One };')
> +    ])
> +    self.assertBackwardCompatible([
> +        Change('foo/foo.mojom',
> +               old='[Extensible] enum E { [Default] One, Two, };',
> +               new='[Extensible] enum E { One, [Default] Two, };')
> +    ])
> diff --git a/utils/ipc/mojo/public/tools/mojom/const_unittest.py b/utils/ipc/mojo/public/tools/mojom/const_unittest.py
> index cb42dfac3556..e8ed36a7a5bf 100644
> --- a/utils/ipc/mojo/public/tools/mojom/const_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/const_unittest.py
> @@ -1,4 +1,4 @@
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/enum_unittest.py b/utils/ipc/mojo/public/tools/mojom/enum_unittest.py
> index d9005078671e..9269cde526b4 100644
> --- a/utils/ipc/mojo/public/tools/mojom/enum_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/enum_unittest.py
> @@ -1,4 +1,4 @@
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -90,3 +90,31 @@ class EnumTest(MojomParserTestCase):
>      self.assertEqual('F', b.enums[0].mojom_name)
>      self.assertEqual('kFoo', b.enums[0].fields[0].mojom_name)
>      self.assertEqual(37, b.enums[0].fields[0].numeric_value)
> +
> +  def testEnumAttributesAreEnums(self):
> +    """Verifies that enum values in attributes are really enum types."""
> +    a_mojom = 'a.mojom'
> +    self.WriteFile(a_mojom, 'module a; enum E { kFoo, kBar };')
> +    b_mojom = 'b.mojom'
> +    self.WriteFile(
> +        b_mojom, 'module b;'
> +        'import "a.mojom";'
> +        '[MooCow=a.E.kFoo]'
> +        'interface Foo { Foo(); };')
> +    self.ParseMojoms([a_mojom, b_mojom])
> +    b = self.LoadModule(b_mojom)
> +    self.assertEqual(b.interfaces[0].attributes['MooCow'].mojom_name, 'kFoo')
> +
> +  def testConstantAttributes(self):
> +    """Verifies that constants as attributes are translated to the constant."""
> +    a_mojom = 'a.mojom'
> +    self.WriteFile(
> +        a_mojom, 'module a;'
> +        'enum E { kFoo, kBar };'
> +        'const E kB = E.kFoo;'
> +        '[Attr=kB] interface Hello { Foo(); };')
> +    self.ParseMojoms([a_mojom])
> +    a = self.LoadModule(a_mojom)
> +    self.assertEqual(a.interfaces[0].attributes['Attr'].mojom_name, 'kB')
> +    self.assertEquals(a.interfaces[0].attributes['Attr'].value.mojom_name,
> +                      'kFoo')
> diff --git a/utils/ipc/mojo/public/tools/mojom/feature_unittest.py b/utils/ipc/mojo/public/tools/mojom/feature_unittest.py
> new file mode 100644
> index 000000000000..5f014e1cfe9a
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/mojom/feature_unittest.py
> @@ -0,0 +1,84 @@
> +# Copyright 2023 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +
> +from mojom_parser_test_case import MojomParserTestCase
> +
> +
> +class FeatureTest(MojomParserTestCase):
> +  """Tests feature parsing behavior."""
> +  def testFeatureOff(self):
> +    """Verifies basic parsing of feature types."""
> +    types = self.ExtractTypes("""
> +      // e.g. BASE_DECLARE_FEATURE(kFeature);
> +      [AttributeOne=ValueOne]
> +      feature kFeature {
> +        // BASE_FEATURE(kFeature,"MyFeature",
> +        //     base::FEATURE_DISABLED_BY_DEFAULT);
> +        const string name = "MyFeature";
> +        const bool default_state = false;
> +      };
> +    """)
> +    self.assertEqual('name', types['kFeature'].constants[0].mojom_name)
> +    self.assertEqual('"MyFeature"', types['kFeature'].constants[0].value)
> +    self.assertEqual('default_state', types['kFeature'].constants[1].mojom_name)
> +    self.assertEqual('false', types['kFeature'].constants[1].value)
> +
> +  def testFeatureOn(self):
> +    """Verifies basic parsing of feature types."""
> +    types = self.ExtractTypes("""
> +      // e.g. BASE_DECLARE_FEATURE(kFeature);
> +      feature kFeature {
> +        // BASE_FEATURE(kFeature,"MyFeature",
> +        //     base::FEATURE_ENABLED_BY_DEFAULT);
> +        const string name = "MyFeature";
> +        const bool default_state = true;
> +      };
> +    """)
> +    self.assertEqual('name', types['kFeature'].constants[0].mojom_name)
> +    self.assertEqual('"MyFeature"', types['kFeature'].constants[0].value)
> +    self.assertEqual('default_state', types['kFeature'].constants[1].mojom_name)
> +    self.assertEqual('true', types['kFeature'].constants[1].value)
> +
> +  def testFeatureWeakKeyword(self):
> +    """Verifies that `feature` is a weak keyword."""
> +    types = self.ExtractTypes("""
> +      // e.g. BASE_DECLARE_FEATURE(kFeature);
> +      [AttributeOne=ValueOne]
> +      feature kFeature {
> +        // BASE_FEATURE(kFeature,"MyFeature",
> +        //     base::FEATURE_DISABLED_BY_DEFAULT);
> +        const string name = "MyFeature";
> +        const bool default_state = false;
> +      };
> +      struct MyStruct {
> +         bool feature = true;
> +      };
> +      interface InterfaceName {
> +         Method(string feature) => (int32 feature);
> +      };
> +    """)
> +    self.assertEqual('name', types['kFeature'].constants[0].mojom_name)
> +    self.assertEqual('"MyFeature"', types['kFeature'].constants[0].value)
> +    self.assertEqual('default_state', types['kFeature'].constants[1].mojom_name)
> +    self.assertEqual('false', types['kFeature'].constants[1].value)
> +
> +  def testFeatureAttributesAreFeatures(self):
> +    """Verifies that feature values in attributes are really feature types."""
> +    a_mojom = 'a.mojom'
> +    self.WriteFile(
> +        a_mojom, 'module a;'
> +        'feature F { const string name = "f";'
> +        'const bool default_state = false; };')
> +    b_mojom = 'b.mojom'
> +    self.WriteFile(
> +        b_mojom, 'module b;'
> +        'import "a.mojom";'
> +        'feature G'
> +        '{const string name = "g"; const bool default_state = false;};'
> +        '[Attri=a.F] interface Foo { Foo(); };'
> +        '[Boink=G] interface Bar {};')
> +    self.ParseMojoms([a_mojom, b_mojom])
> +    b = self.LoadModule(b_mojom)
> +    self.assertEqual(b.interfaces[0].attributes['Attri'].mojom_name, 'F')
> +    self.assertEqual(b.interfaces[1].attributes['Boink'].mojom_name, 'G')
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/BUILD.gn b/utils/ipc/mojo/public/tools/mojom/mojom/BUILD.gn
> index 51facc0ccb84..a0edf0eb5d2c 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/BUILD.gn
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/BUILD.gn
> @@ -1,4 +1,4 @@
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -8,6 +8,7 @@ group("mojom") {
>      "error.py",
>      "fileutil.py",
>      "generate/__init__.py",
> +    "generate/check.py",
>      "generate/generator.py",
>      "generate/module.py",
>      "generate/pack.py",
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/error.py b/utils/ipc/mojo/public/tools/mojom/mojom/error.py
> index 8a1e03da5c1d..dd53b835a49e 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/error.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/error.py
> @@ -1,4 +1,4 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/fileutil.py b/utils/ipc/mojo/public/tools/mojom/mojom/fileutil.py
> index bf626f54798c..124f12c134b9 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/fileutil.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/fileutil.py
> @@ -1,9 +1,8 @@
> -# Copyright 2015 The Chromium Authors. All rights reserved.
> +# Copyright 2015 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
>  import errno
> -import imp
>  import os.path
>  import sys
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/fileutil_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/fileutil_unittest.py
> index ff5753a29114..c93d22898d29 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/fileutil_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/fileutil_unittest.py
> @@ -1,20 +1,17 @@
> -# Copyright 2015 The Chromium Authors. All rights reserved.
> +# Copyright 2015 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import imp
>  import os.path
>  import shutil
> -import sys
>  import tempfile
>  import unittest
>  
>  from mojom import fileutil
>  
> -
>  class FileUtilTest(unittest.TestCase):
>    def testEnsureDirectoryExists(self):
> -    """Test that EnsureDirectoryExists fuctions correctly."""
> +    """Test that EnsureDirectoryExists functions correctly."""
>  
>      temp_dir = tempfile.mkdtemp()
>      try:
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/check.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/check.py
> new file mode 100644
> index 000000000000..1efe2022342b
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/check.py
> @@ -0,0 +1,26 @@
> +# Copyright 2022 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +"""Code shared by the various pre-generation mojom checkers."""
> +
> +
> +class CheckException(Exception):
> +  def __init__(self, module, message):
> +    self.module = module
> +    self.message = message
> +    super().__init__(self.message)
> +
> +  def __str__(self):
> +    return "Failed mojo pre-generation check for {}:\n{}".format(
> +        self.module.path, self.message)
> +
> +
> +class Check:
> +  def __init__(self, module):
> +    self.module = module
> +
> +  def CheckModule(self):
> +    """ Subclass should return True if its Checks pass, and throw an
> +    exception otherwise. CheckModule will be called immediately before
> +    mojom.generate.Generator.GenerateFiles()"""
> +    raise NotImplementedError("Subclasses must override/implement this method")
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/constant_resolver.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/constant_resolver.py
> deleted file mode 100644
> index 0dfd996e355d..000000000000
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/constant_resolver.py
> +++ /dev/null
> @@ -1,93 +0,0 @@
> -# Copyright 2015 The Chromium Authors. All rights reserved.
> -# Use of this source code is governed by a BSD-style license that can be
> -# found in the LICENSE file.
> -"""Resolves the values used for constants and enums."""
> -
> -from itertools import ifilter
> -
> -from mojom.generate import module as mojom
> -
> -
> -def ResolveConstants(module, expression_to_text):
> -  in_progress = set()
> -  computed = set()
> -
> -  def GetResolvedValue(named_value):
> -    assert isinstance(named_value, (mojom.EnumValue, mojom.ConstantValue))
> -    if isinstance(named_value, mojom.EnumValue):
> -      field = next(
> -          ifilter(lambda field: field.name == named_value.name,
> -                  named_value.enum.fields), None)
> -      if not field:
> -        raise RuntimeError(
> -            'Unable to get computed value for field %s of enum %s' %
> -            (named_value.name, named_value.enum.name))
> -      if field not in computed:
> -        ResolveEnum(named_value.enum)
> -      return field.resolved_value
> -    else:
> -      ResolveConstant(named_value.constant)
> -      named_value.resolved_value = named_value.constant.resolved_value
> -      return named_value.resolved_value
> -
> -  def ResolveConstant(constant):
> -    if constant in computed:
> -      return
> -    if constant in in_progress:
> -      raise RuntimeError('Circular dependency for constant: %s' % constant.name)
> -    in_progress.add(constant)
> -    if isinstance(constant.value, (mojom.EnumValue, mojom.ConstantValue)):
> -      resolved_value = GetResolvedValue(constant.value)
> -    else:
> -      resolved_value = expression_to_text(constant.value)
> -    constant.resolved_value = resolved_value
> -    in_progress.remove(constant)
> -    computed.add(constant)
> -
> -  def ResolveEnum(enum):
> -    def ResolveEnumField(enum, field, default_value):
> -      if field in computed:
> -        return
> -      if field in in_progress:
> -        raise RuntimeError('Circular dependency for enum: %s' % enum.name)
> -      in_progress.add(field)
> -      if field.value:
> -        if isinstance(field.value, mojom.EnumValue):
> -          resolved_value = GetResolvedValue(field.value)
> -        elif isinstance(field.value, str):
> -          resolved_value = int(field.value, 0)
> -        else:
> -          raise RuntimeError('Unexpected value: %s' % field.value)
> -      else:
> -        resolved_value = default_value
> -      field.resolved_value = resolved_value
> -      in_progress.remove(field)
> -      computed.add(field)
> -
> -    current_value = 0
> -    for field in enum.fields:
> -      ResolveEnumField(enum, field, current_value)
> -      current_value = field.resolved_value + 1
> -
> -  for constant in module.constants:
> -    ResolveConstant(constant)
> -
> -  for enum in module.enums:
> -    ResolveEnum(enum)
> -
> -  for struct in module.structs:
> -    for constant in struct.constants:
> -      ResolveConstant(constant)
> -    for enum in struct.enums:
> -      ResolveEnum(enum)
> -    for field in struct.fields:
> -      if isinstance(field.default, (mojom.ConstantValue, mojom.EnumValue)):
> -        field.default.resolved_value = GetResolvedValue(field.default)
> -
> -  for interface in module.interfaces:
> -    for constant in interface.constants:
> -      ResolveConstant(constant)
> -    for enum in interface.enums:
> -      ResolveEnum(enum)
> -
> -  return module
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/generator.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/generator.py
> index 4a1c73fcf82f..96fe3a2d0920 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/generator.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/generator.py
> @@ -1,4 +1,4 @@
> -# Copyright 2013 The Chromium Authors. All rights reserved.
> +# Copyright 2013 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Code shared by the various language-specific code generators."""
> @@ -97,7 +97,7 @@ def ToLowerSnakeCase(identifier):
>    return _ToSnakeCase(identifier, upper=False)
>  
>  
> -class Stylizer(object):
> +class Stylizer:
>    """Stylizers specify naming rules to map mojom names to names in generated
>    code. For example, if you would like method_name in mojom to be mapped to
>    MethodName in the generated code, you need to define a subclass of Stylizer
> @@ -130,6 +130,9 @@ class Stylizer(object):
>    def StylizeEnum(self, mojom_name):
>      return mojom_name
>  
> +  def StylizeFeature(self, mojom_name):
> +    return mojom_name
> +
>    def StylizeModule(self, mojom_namespace):
>      return mojom_namespace
>  
> @@ -233,7 +236,7 @@ def AddComputedData(module):
>      _AddInterfaceComputedData(interface)
>  
>  
> -class Generator(object):
> +class Generator:
>    # Pass |output_dir| to emit files to disk. Omit |output_dir| to echo all
>    # files to stdout.
>    def __init__(self,
> @@ -243,7 +246,6 @@ class Generator(object):
>                 variant=None,
>                 bytecode_path=None,
>                 for_blink=False,
> -               js_bindings_mode="new",
>                 js_generate_struct_deserializers=False,
>                 export_attribute=None,
>                 export_header=None,
> @@ -262,7 +264,6 @@ class Generator(object):
>      self.variant = variant
>      self.bytecode_path = bytecode_path
>      self.for_blink = for_blink
> -    self.js_bindings_mode = js_bindings_mode
>      self.js_generate_struct_deserializers = js_generate_struct_deserializers
>      self.export_attribute = export_attribute
>      self.export_header = export_header
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/generator_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/generator_unittest.py
> index 32c884a8c02e..7143e07c4d7e 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/generator_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/generator_unittest.py
> @@ -1,13 +1,12 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import imp
> +import importlib.util
>  import os.path
>  import sys
>  import unittest
>  
> -
>  def _GetDirAbove(dirname):
>    """Returns the directory "above" this file containing |dirname| (which must
>    also be "above" this file)."""
> @@ -20,12 +19,11 @@ def _GetDirAbove(dirname):
>  
>  
>  try:
> -  imp.find_module("mojom")
> +  importlib.util.find_spec("mojom")
>  except ImportError:
>    sys.path.append(os.path.join(_GetDirAbove("pylib"), "pylib"))
>  from mojom.generate import generator
>  
> -
>  class StringManipulationTest(unittest.TestCase):
>    """generator contains some string utilities, this tests only those."""
>  
> @@ -69,6 +67,5 @@ class StringManipulationTest(unittest.TestCase):
>      self.assertEquals("SNAKE_D3D11_CASE",
>                        generator.ToUpperSnakeCase("snakeD3d11Case"))
>  
> -
>  if __name__ == "__main__":
>    unittest.main()
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/module.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/module.py
> index 9bdb28e05f65..ca71059d53b1 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/module.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/module.py
> @@ -1,4 +1,4 @@
> -# Copyright 2013 The Chromium Authors. All rights reserved.
> +# Copyright 2013 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -12,15 +12,14 @@
>  # method = interface.AddMethod('Tat', 0)
>  # method.AddParameter('baz', 0, mojom.INT32)
>  
> -import sys
> -if sys.version_info.major == 2:
> -  import cPickle as pickle
> -else:
> -  import pickle
> +import pickle
> +from collections import OrderedDict
>  from uuid import UUID
>  
> +# pylint: disable=raise-missing-from
>  
> -class BackwardCompatibilityChecker(object):
> +
> +class BackwardCompatibilityChecker:
>    """Used for memoization while recursively checking two type definitions for
>    backward-compatibility."""
>  
> @@ -64,23 +63,20 @@ def Repr(obj, as_ref=True):
>      return obj.Repr(as_ref=as_ref)
>    # Since we cannot implement Repr for existing container types, we
>    # handle them here.
> -  elif isinstance(obj, list):
> +  if isinstance(obj, list):
>      if not obj:
>        return '[]'
> -    else:
> -      return ('[\n%s\n]' % (',\n'.join(
> -          '    %s' % Repr(elem, as_ref).replace('\n', '\n    ')
> -          for elem in obj)))
> -  elif isinstance(obj, dict):
> +    return ('[\n%s\n]' %
> +            (',\n'.join('    %s' % Repr(elem, as_ref).replace('\n', '\n    ')
> +                        for elem in obj)))
> +  if isinstance(obj, dict):
>      if not obj:
>        return '{}'
> -    else:
> -      return ('{\n%s\n}' % (',\n'.join(
> -          '    %s: %s' % (Repr(key, as_ref).replace('\n', '\n    '),
> -                          Repr(val, as_ref).replace('\n', '\n    '))
> -          for key, val in obj.items())))
> -  else:
> -    return repr(obj)
> +    return ('{\n%s\n}' % (',\n'.join('    %s: %s' %
> +                                     (Repr(key, as_ref).replace('\n', '\n    '),
> +                                      Repr(val, as_ref).replace('\n', '\n    '))
> +                                     for key, val in obj.items())))
> +  return repr(obj)
>  
>  
>  def GenericRepr(obj, names):
> @@ -104,7 +100,7 @@ def GenericRepr(obj, names):
>        ReprIndent(name, as_ref) for (name, as_ref) in names.items()))
>  
>  
> -class Kind(object):
> +class Kind:
>    """Kind represents a type (e.g. int8, string).
>  
>    Attributes:
> @@ -112,16 +108,43 @@ class Kind(object):
>      module: {Module} The defining module. Set to None for built-in types.
>      parent_kind: The enclosing type. For example, an enum defined
>          inside an interface has that interface as its parent. May be None.
> +    is_nullable: True if the type is nullable.
>    """
>  
> -  def __init__(self, spec=None, module=None):
> +  def __init__(self, spec=None, is_nullable=False, module=None):
>      self.spec = spec
>      self.module = module
>      self.parent_kind = None
> +    self.is_nullable = is_nullable
> +    self.shared_definition = {}
> +
> +  @classmethod
> +  def AddSharedProperty(cls, name):
> +    """Adds a property |name| to |cls|, which accesses the corresponding item in
> +       |shared_definition|.
> +
> +       The reason of adding such indirection is to enable sharing definition
> +       between a reference kind and its nullable variation. For example:
> +         a = Struct('test_struct_1')
> +         b = a.MakeNullableKind()
> +         a.name = 'test_struct_2'
> +         print(b.name)  # Outputs 'test_struct_2'.
> +    """
> +    def Get(self):
> +      try:
> +        return self.shared_definition[name]
> +      except KeyError:  # Must raise AttributeError if property doesn't exist.
> +        raise AttributeError
> +
> +    def Set(self, value):
> +      self.shared_definition[name] = value
> +
> +    setattr(cls, name, property(Get, Set))
>  
>    def Repr(self, as_ref=True):
>      # pylint: disable=unused-argument
> -    return '<%s spec=%r>' % (self.__class__.__name__, self.spec)
> +    return '<%s spec=%r is_nullable=%r>' % (self.__class__.__name__, self.spec,
> +                                            self.is_nullable)
>  
>    def __repr__(self):
>      # Gives us a decent __repr__ for all kinds.
> @@ -130,7 +153,8 @@ class Kind(object):
>    def __eq__(self, rhs):
>      # pylint: disable=unidiomatic-typecheck
>      return (type(self) == type(rhs)
> -            and (self.spec, self.parent_kind) == (rhs.spec, rhs.parent_kind))
> +            and (self.spec, self.parent_kind, self.is_nullable)
> +            == (rhs.spec, rhs.parent_kind, rhs.is_nullable))
>  
>    def __hash__(self):
>      # TODO(crbug.com/1060471): Remove this and other __hash__ methods on Kind
> @@ -138,32 +162,113 @@ class Kind(object):
>      # some primitive Kinds as dict keys. The default hash (object identity)
>      # breaks these dicts when a pickled Module instance is unpickled and used
>      # during a subsequent run of the parser.
> -    return hash((self.spec, self.parent_kind))
> +    return hash((self.spec, self.parent_kind, self.is_nullable))
>  
>    # pylint: disable=unused-argument
>    def IsBackwardCompatible(self, rhs, checker):
>      return self == rhs
>  
>  
> +class ValueKind(Kind):
> +  """ValueKind represents values that aren't reference kinds.
> +
> +  The primary difference is the wire representation for nullable value kinds
> +  still reserves space for the value type itself, even if that value itself
> +  is logically null.
> +  """
> +  def __init__(self, spec=None, is_nullable=False, module=None):
> +    assert spec is None or is_nullable == spec.startswith('?')
> +    Kind.__init__(self, spec, is_nullable, module)
> +
> +  def MakeNullableKind(self):
> +    assert not self.is_nullable
> +
> +    if self == BOOL:
> +      return NULLABLE_BOOL
> +    if self == INT8:
> +      return NULLABLE_INT8
> +    if self == INT16:
> +      return NULLABLE_INT16
> +    if self == INT32:
> +      return NULLABLE_INT32
> +    if self == INT64:
> +      return NULLABLE_INT64
> +    if self == UINT8:
> +      return NULLABLE_UINT8
> +    if self == UINT16:
> +      return NULLABLE_UINT16
> +    if self == UINT32:
> +      return NULLABLE_UINT32
> +    if self == UINT64:
> +      return NULLABLE_UINT64
> +    if self == FLOAT:
> +      return NULLABLE_FLOAT
> +    if self == DOUBLE:
> +      return NULLABLE_DOUBLE
> +
> +    nullable_kind = type(self)()
> +    nullable_kind.shared_definition = self.shared_definition
> +    if self.spec is not None:
> +      nullable_kind.spec = '?' + self.spec
> +    nullable_kind.is_nullable = True
> +    nullable_kind.parent_kind = self.parent_kind
> +    nullable_kind.module = self.module
> +
> +    return nullable_kind
> +
> +  def MakeUnnullableKind(self):
> +    assert self.is_nullable
> +
> +    if self == NULLABLE_BOOL:
> +      return BOOL
> +    if self == NULLABLE_INT8:
> +      return INT8
> +    if self == NULLABLE_INT16:
> +      return INT16
> +    if self == NULLABLE_INT32:
> +      return INT32
> +    if self == NULLABLE_INT64:
> +      return INT64
> +    if self == NULLABLE_UINT8:
> +      return UINT8
> +    if self == NULLABLE_UINT16:
> +      return UINT16
> +    if self == NULLABLE_UINT32:
> +      return UINT32
> +    if self == NULLABLE_UINT64:
> +      return UINT64
> +    if self == NULLABLE_FLOAT:
> +      return FLOAT
> +    if self == NULLABLE_DOUBLE:
> +      return DOUBLE
> +
> +    nullable_kind = type(self)()
> +    nullable_kind.shared_definition = self.shared_definition
> +    if self.spec is not None:
> +      nullable_kind.spec = self.spec[1:]
> +    nullable_kind.is_nullable = False
> +    nullable_kind.parent_kind = self.parent_kind
> +    nullable_kind.module = self.module
> +
> +    return nullable_kind
> +
> +  def __eq__(self, rhs):
> +    return (isinstance(rhs, ValueKind) and super().__eq__(rhs))
> +
> +  def __hash__(self):  # pylint: disable=useless-super-delegation
> +    return super().__hash__()
> +
> +
>  class ReferenceKind(Kind):
>    """ReferenceKind represents pointer and handle types.
>  
>    A type is nullable if null (for pointer types) or invalid handle (for handle
>    types) is a legal value for the type.
> -
> -  Attributes:
> -    is_nullable: True if the type is nullable.
>    """
>  
>    def __init__(self, spec=None, is_nullable=False, module=None):
>      assert spec is None or is_nullable == spec.startswith('?')
> -    Kind.__init__(self, spec, module)
> -    self.is_nullable = is_nullable
> -    self.shared_definition = {}
> -
> -  def Repr(self, as_ref=True):
> -    return '<%s spec=%r is_nullable=%r>' % (self.__class__.__name__, self.spec,
> -                                            self.is_nullable)
> +    Kind.__init__(self, spec, is_nullable, module)
>  
>    def MakeNullableKind(self):
>      assert not self.is_nullable
> @@ -193,55 +298,65 @@ class ReferenceKind(Kind):
>  
>      return nullable_kind
>  
> -  @classmethod
> -  def AddSharedProperty(cls, name):
> -    """Adds a property |name| to |cls|, which accesses the corresponding item in
> -       |shared_definition|.
> +  def MakeUnnullableKind(self):
> +    assert self.is_nullable
>  
> -       The reason of adding such indirection is to enable sharing definition
> -       between a reference kind and its nullable variation. For example:
> -         a = Struct('test_struct_1')
> -         b = a.MakeNullableKind()
> -         a.name = 'test_struct_2'
> -         print(b.name)  # Outputs 'test_struct_2'.
> -    """
> +    if self == NULLABLE_STRING:
> +      return STRING
> +    if self == NULLABLE_HANDLE:
> +      return HANDLE
> +    if self == NULLABLE_DCPIPE:
> +      return DCPIPE
> +    if self == NULLABLE_DPPIPE:
> +      return DPPIPE
> +    if self == NULLABLE_MSGPIPE:
> +      return MSGPIPE
> +    if self == NULLABLE_SHAREDBUFFER:
> +      return SHAREDBUFFER
> +    if self == NULLABLE_PLATFORMHANDLE:
> +      return PLATFORMHANDLE
>  
> -    def Get(self):
> -      try:
> -        return self.shared_definition[name]
> -      except KeyError:  # Must raise AttributeError if property doesn't exist.
> -        raise AttributeError
> +    unnullable_kind = type(self)()
> +    unnullable_kind.shared_definition = self.shared_definition
> +    if self.spec is not None:
> +      assert self.spec[0] == '?'
> +      unnullable_kind.spec = self.spec[1:]
> +    unnullable_kind.is_nullable = False
> +    unnullable_kind.parent_kind = self.parent_kind
> +    unnullable_kind.module = self.module
>  
> -    def Set(self, value):
> -      self.shared_definition[name] = value
> -
> -    setattr(cls, name, property(Get, Set))
> +    return unnullable_kind
>  
>    def __eq__(self, rhs):
> -    return (isinstance(rhs, ReferenceKind)
> -            and super(ReferenceKind, self).__eq__(rhs)
> -            and self.is_nullable == rhs.is_nullable)
> +    return (isinstance(rhs, ReferenceKind) and super().__eq__(rhs))
>  
> -  def __hash__(self):
> -    return hash((super(ReferenceKind, self).__hash__(), self.is_nullable))
> -
> -  def IsBackwardCompatible(self, rhs, checker):
> -    return (super(ReferenceKind, self).IsBackwardCompatible(rhs, checker)
> -            and self.is_nullable == rhs.is_nullable)
> +  def __hash__(self):  # pylint: disable=useless-super-delegation
> +    return super().__hash__()
>  
>  
>  # Initialize the set of primitive types. These can be accessed by clients.
> -BOOL = Kind('b')
> -INT8 = Kind('i8')
> -INT16 = Kind('i16')
> -INT32 = Kind('i32')
> -INT64 = Kind('i64')
> -UINT8 = Kind('u8')
> -UINT16 = Kind('u16')
> -UINT32 = Kind('u32')
> -UINT64 = Kind('u64')
> -FLOAT = Kind('f')
> -DOUBLE = Kind('d')
> +BOOL = ValueKind('b')
> +INT8 = ValueKind('i8')
> +INT16 = ValueKind('i16')
> +INT32 = ValueKind('i32')
> +INT64 = ValueKind('i64')
> +UINT8 = ValueKind('u8')
> +UINT16 = ValueKind('u16')
> +UINT32 = ValueKind('u32')
> +UINT64 = ValueKind('u64')
> +FLOAT = ValueKind('f')
> +DOUBLE = ValueKind('d')
> +NULLABLE_BOOL = ValueKind('?b', True)
> +NULLABLE_INT8 = ValueKind('?i8', True)
> +NULLABLE_INT16 = ValueKind('?i16', True)
> +NULLABLE_INT32 = ValueKind('?i32', True)
> +NULLABLE_INT64 = ValueKind('?i64', True)
> +NULLABLE_UINT8 = ValueKind('?u8', True)
> +NULLABLE_UINT16 = ValueKind('?u16', True)
> +NULLABLE_UINT32 = ValueKind('?u32', True)
> +NULLABLE_UINT64 = ValueKind('?u64', True)
> +NULLABLE_FLOAT = ValueKind('?f', True)
> +NULLABLE_DOUBLE = ValueKind('?d', True)
>  STRING = ReferenceKind('s')
>  HANDLE = ReferenceKind('h')
>  DCPIPE = ReferenceKind('h:d:c')
> @@ -270,6 +385,17 @@ PRIMITIVES = (
>      UINT64,
>      FLOAT,
>      DOUBLE,
> +    NULLABLE_BOOL,
> +    NULLABLE_INT8,
> +    NULLABLE_INT16,
> +    NULLABLE_INT32,
> +    NULLABLE_INT64,
> +    NULLABLE_UINT8,
> +    NULLABLE_UINT16,
> +    NULLABLE_UINT32,
> +    NULLABLE_UINT64,
> +    NULLABLE_FLOAT,
> +    NULLABLE_DOUBLE,
>      STRING,
>      HANDLE,
>      DCPIPE,
> @@ -291,12 +417,17 @@ ATTRIBUTE_DEFAULT = 'Default'
>  ATTRIBUTE_EXTENSIBLE = 'Extensible'
>  ATTRIBUTE_NO_INTERRUPT = 'NoInterrupt'
>  ATTRIBUTE_STABLE = 'Stable'
> +ATTRIBUTE_SUPPORTS_URGENT = 'SupportsUrgent'
>  ATTRIBUTE_SYNC = 'Sync'
>  ATTRIBUTE_UNLIMITED_SIZE = 'UnlimitedSize'
>  ATTRIBUTE_UUID = 'Uuid'
> +ATTRIBUTE_SERVICE_SANDBOX = 'ServiceSandbox'
> +ATTRIBUTE_REQUIRE_CONTEXT = 'RequireContext'
> +ATTRIBUTE_ALLOWED_CONTEXT = 'AllowedContext'
> +ATTRIBUTE_RUNTIME_FEATURE = 'RuntimeFeature'
>  
>  
> -class NamedValue(object):
> +class NamedValue:
>    def __init__(self, module, parent_kind, mojom_name):
>      self.module = module
>      self.parent_kind = parent_kind
> @@ -316,7 +447,7 @@ class NamedValue(object):
>      return hash((self.parent_kind, self.mojom_name))
>  
>  
> -class BuiltinValue(object):
> +class BuiltinValue:
>    def __init__(self, value):
>      self.value = value
>  
> @@ -350,7 +481,7 @@ class EnumValue(NamedValue):
>      return self.field.name
>  
>  
> -class Constant(object):
> +class Constant:
>    def __init__(self, mojom_name=None, kind=None, value=None, parent_kind=None):
>      self.mojom_name = mojom_name
>      self.name = None
> @@ -368,7 +499,7 @@ class Constant(object):
>                                         rhs.parent_kind))
>  
>  
> -class Field(object):
> +class Field:
>    def __init__(self,
>                 mojom_name=None,
>                 kind=None,
> @@ -414,7 +545,18 @@ class StructField(Field):
>  
>  
>  class UnionField(Field):
> -  pass
> +  def __init__(self,
> +               mojom_name=None,
> +               kind=None,
> +               ordinal=None,
> +               default=None,
> +               attributes=None):
> +    Field.__init__(self, mojom_name, kind, ordinal, default, attributes)
> +
> +  @property
> +  def is_default(self):
> +    return self.attributes.get(ATTRIBUTE_DEFAULT, False) \
> +        if self.attributes else False
>  
>  
>  def _IsFieldBackwardCompatible(new_field, old_field, checker):
> @@ -424,6 +566,38 @@ def _IsFieldBackwardCompatible(new_field, old_field, checker):
>    return checker.IsBackwardCompatible(new_field.kind, old_field.kind)
>  
>  
> +class Feature(ReferenceKind):
> +  """A runtime enabled feature defined from mojom.
> +
> +  Attributes:
> +    mojom_name: {str} The name of the feature type as defined in mojom.
> +    name: {str} The stylized name. (Note: not the "name" used by FeatureList.)
> +    constants: {List[Constant]} The constants defined in the feature scope.
> +    attributes: {dict} Additional information about the feature.
> +  """
> +
> +  Kind.AddSharedProperty('mojom_name')
> +  Kind.AddSharedProperty('name')
> +  Kind.AddSharedProperty('constants')
> +  Kind.AddSharedProperty('attributes')
> +
> +  def __init__(self, mojom_name=None, module=None, attributes=None):
> +    if mojom_name is not None:
> +      spec = 'x:' + mojom_name
> +    else:
> +      spec = None
> +    ReferenceKind.__init__(self, spec, False, module)
> +    self.mojom_name = mojom_name
> +    self.name = None
> +    self.constants = []
> +    self.attributes = attributes
> +
> +  def Stylize(self, stylizer):
> +    self.name = stylizer.StylizeFeature(self.mojom_name)
> +    for constant in self.constants:
> +      constant.Stylize(stylizer)
> +
> +
>  class Struct(ReferenceKind):
>    """A struct with typed fields.
>  
> @@ -441,14 +615,14 @@ class Struct(ReferenceKind):
>          if it's a native struct.
>    """
>  
> -  ReferenceKind.AddSharedProperty('mojom_name')
> -  ReferenceKind.AddSharedProperty('name')
> -  ReferenceKind.AddSharedProperty('native_only')
> -  ReferenceKind.AddSharedProperty('custom_serializer')
> -  ReferenceKind.AddSharedProperty('fields')
> -  ReferenceKind.AddSharedProperty('enums')
> -  ReferenceKind.AddSharedProperty('constants')
> -  ReferenceKind.AddSharedProperty('attributes')
> +  Kind.AddSharedProperty('mojom_name')
> +  Kind.AddSharedProperty('name')
> +  Kind.AddSharedProperty('native_only')
> +  Kind.AddSharedProperty('custom_serializer')
> +  Kind.AddSharedProperty('fields')
> +  Kind.AddSharedProperty('enums')
> +  Kind.AddSharedProperty('constants')
> +  Kind.AddSharedProperty('attributes')
>  
>    def __init__(self, mojom_name=None, module=None, attributes=None):
>      if mojom_name is not None:
> @@ -470,12 +644,11 @@ class Struct(ReferenceKind):
>        return '<%s mojom_name=%r module=%s>' % (self.__class__.__name__,
>                                                 self.mojom_name,
>                                                 Repr(self.module, as_ref=True))
> -    else:
> -      return GenericRepr(self, {
> -          'mojom_name': False,
> -          'fields': False,
> -          'module': True
> -      })
> +    return GenericRepr(self, {
> +        'mojom_name': False,
> +        'fields': False,
> +        'module': True
> +    })
>  
>    def AddField(self,
>                 mojom_name,
> @@ -496,13 +669,13 @@ class Struct(ReferenceKind):
>      for constant in self.constants:
>        constant.Stylize(stylizer)
>  
> -  def IsBackwardCompatible(self, older_struct, checker):
> -    """This struct is backward-compatible with older_struct if and only if all
> -    of the following conditions hold:
> +  def IsBackwardCompatible(self, rhs, checker):
> +    """This struct is backward-compatible with rhs (older_struct) if and only if
> +    all of the following conditions hold:
>        - Any newly added field is tagged with a [MinVersion] attribute specifying
>          a version number greater than all previously used [MinVersion]
>          attributes within the struct.
> -      - All fields present in older_struct remain present in the new struct,
> +      - All fields present in rhs remain present in the new struct,
>          with the same ordinal position, same optional or non-optional status,
>          same (or backward-compatible) type and where applicable, the same
>          [MinVersion] attribute value.
> @@ -521,7 +694,7 @@ class Struct(ReferenceKind):
>        return fields_by_ordinal
>  
>      new_fields = buildOrdinalFieldMap(self)
> -    old_fields = buildOrdinalFieldMap(older_struct)
> +    old_fields = buildOrdinalFieldMap(rhs)
>      if len(new_fields) < len(old_fields):
>        # At least one field was removed, which is not OK.
>        return False
> @@ -574,11 +747,18 @@ class Struct(ReferenceKind):
>        prefix = self.module.GetNamespacePrefix()
>      return '%s%s' % (prefix, self.mojom_name)
>  
> +  def _tuple(self):
> +    return (self.mojom_name, self.native_only, self.fields, self.constants,
> +            self.attributes)
> +
>    def __eq__(self, rhs):
> -    return (isinstance(rhs, Struct) and
> -            (self.mojom_name, self.native_only, self.fields, self.constants,
> -             self.attributes) == (rhs.mojom_name, rhs.native_only, rhs.fields,
> -                                  rhs.constants, rhs.attributes))
> +    return isinstance(rhs, Struct) and self._tuple() == rhs._tuple()
> +
> +  def __lt__(self, rhs):
> +    if not isinstance(self, type(rhs)):
> +      return str(type(self)) < str(type(rhs))
> +
> +    return self._tuple() < rhs._tuple()
>  
>    def __hash__(self):
>      return id(self)
> @@ -595,10 +775,11 @@ class Union(ReferenceKind):
>          which Java class name to use to represent it in the generated
>          bindings.
>    """
> -  ReferenceKind.AddSharedProperty('mojom_name')
> -  ReferenceKind.AddSharedProperty('name')
> -  ReferenceKind.AddSharedProperty('fields')
> -  ReferenceKind.AddSharedProperty('attributes')
> +  Kind.AddSharedProperty('mojom_name')
> +  Kind.AddSharedProperty('name')
> +  Kind.AddSharedProperty('fields')
> +  Kind.AddSharedProperty('attributes')
> +  Kind.AddSharedProperty('default_field')
>  
>    def __init__(self, mojom_name=None, module=None, attributes=None):
>      if mojom_name is not None:
> @@ -610,14 +791,14 @@ class Union(ReferenceKind):
>      self.name = None
>      self.fields = []
>      self.attributes = attributes
> +    self.default_field = None
>  
>    def Repr(self, as_ref=True):
>      if as_ref:
>        return '<%s spec=%r is_nullable=%r fields=%s>' % (
>            self.__class__.__name__, self.spec, self.is_nullable, Repr(
>                self.fields))
> -    else:
> -      return GenericRepr(self, {'fields': True, 'is_nullable': False})
> +    return GenericRepr(self, {'fields': True, 'is_nullable': False})
>  
>    def AddField(self, mojom_name, kind, ordinal=None, attributes=None):
>      field = UnionField(mojom_name, kind, ordinal, None, attributes)
> @@ -629,13 +810,13 @@ class Union(ReferenceKind):
>      for field in self.fields:
>        field.Stylize(stylizer)
>  
> -  def IsBackwardCompatible(self, older_union, checker):
> -    """This union is backward-compatible with older_union if and only if all
> -    of the following conditions hold:
> +  def IsBackwardCompatible(self, rhs, checker):
> +    """This union is backward-compatible with rhs (older_union) if and only if
> +    all of the following conditions hold:
>        - Any newly added field is tagged with a [MinVersion] attribute specifying
>          a version number greater than all previously used [MinVersion]
>          attributes within the union.
> -      - All fields present in older_union remain present in the new union,
> +      - All fields present in rhs remain present in the new union,
>          with the same ordinal value, same optional or non-optional status,
>          same (or backward-compatible) type, and where applicable, the same
>          [MinVersion] attribute value.
> @@ -651,7 +832,7 @@ class Union(ReferenceKind):
>        return fields_by_ordinal
>  
>      new_fields = buildOrdinalFieldMap(self)
> -    old_fields = buildOrdinalFieldMap(older_union)
> +    old_fields = buildOrdinalFieldMap(rhs)
>      if len(new_fields) < len(old_fields):
>        # At least one field was removed, which is not OK.
>        return False
> @@ -677,6 +858,11 @@ class Union(ReferenceKind):
>  
>      return True
>  
> +  @property
> +  def extensible(self):
> +    return self.attributes.get(ATTRIBUTE_EXTENSIBLE, False) \
> +        if self.attributes else False
> +
>    @property
>    def stable(self):
>      return self.attributes.get(ATTRIBUTE_STABLE, False) \
> @@ -690,10 +876,17 @@ class Union(ReferenceKind):
>        prefix = self.module.GetNamespacePrefix()
>      return '%s%s' % (prefix, self.mojom_name)
>  
> +  def _tuple(self):
> +    return (self.mojom_name, self.fields, self.attributes)
> +
>    def __eq__(self, rhs):
> -    return (isinstance(rhs, Union) and
> -            (self.mojom_name, self.fields,
> -             self.attributes) == (rhs.mojom_name, rhs.fields, rhs.attributes))
> +    return isinstance(rhs, Union) and self._tuple() == rhs._tuple()
> +
> +  def __lt__(self, rhs):
> +    if not isinstance(self, type(rhs)):
> +      return str(type(self)) < str(type(rhs))
> +
> +    return self._tuple() < rhs._tuple()
>  
>    def __hash__(self):
>      return id(self)
> @@ -707,8 +900,8 @@ class Array(ReferenceKind):
>      length: The number of elements. None if unknown.
>    """
>  
> -  ReferenceKind.AddSharedProperty('kind')
> -  ReferenceKind.AddSharedProperty('length')
> +  Kind.AddSharedProperty('kind')
> +  Kind.AddSharedProperty('length')
>  
>    def __init__(self, kind=None, length=None):
>      if kind is not None:
> @@ -728,12 +921,11 @@ class Array(ReferenceKind):
>        return '<%s spec=%r is_nullable=%r kind=%s length=%r>' % (
>            self.__class__.__name__, self.spec, self.is_nullable, Repr(
>                self.kind), self.length)
> -    else:
> -      return GenericRepr(self, {
> -          'kind': True,
> -          'length': False,
> -          'is_nullable': False
> -      })
> +    return GenericRepr(self, {
> +        'kind': True,
> +        'length': False,
> +        'is_nullable': False
> +    })
>  
>    def __eq__(self, rhs):
>      return (isinstance(rhs, Array)
> @@ -754,8 +946,8 @@ class Map(ReferenceKind):
>      key_kind: {Kind} The type of the keys. May be None.
>      value_kind: {Kind} The type of the elements. May be None.
>    """
> -  ReferenceKind.AddSharedProperty('key_kind')
> -  ReferenceKind.AddSharedProperty('value_kind')
> +  Kind.AddSharedProperty('key_kind')
> +  Kind.AddSharedProperty('value_kind')
>  
>    def __init__(self, key_kind=None, value_kind=None):
>      if (key_kind is not None and value_kind is not None):
> @@ -780,8 +972,7 @@ class Map(ReferenceKind):
>        return '<%s spec=%r is_nullable=%r key_kind=%s value_kind=%s>' % (
>            self.__class__.__name__, self.spec, self.is_nullable,
>            Repr(self.key_kind), Repr(self.value_kind))
> -    else:
> -      return GenericRepr(self, {'key_kind': True, 'value_kind': True})
> +    return GenericRepr(self, {'key_kind': True, 'value_kind': True})
>  
>    def __eq__(self, rhs):
>      return (isinstance(rhs, Map) and
> @@ -797,7 +988,7 @@ class Map(ReferenceKind):
>  
>  
>  class PendingRemote(ReferenceKind):
> -  ReferenceKind.AddSharedProperty('kind')
> +  Kind.AddSharedProperty('kind')
>  
>    def __init__(self, kind=None):
>      if kind is not None:
> @@ -822,7 +1013,7 @@ class PendingRemote(ReferenceKind):
>  
>  
>  class PendingReceiver(ReferenceKind):
> -  ReferenceKind.AddSharedProperty('kind')
> +  Kind.AddSharedProperty('kind')
>  
>    def __init__(self, kind=None):
>      if kind is not None:
> @@ -847,7 +1038,7 @@ class PendingReceiver(ReferenceKind):
>  
>  
>  class PendingAssociatedRemote(ReferenceKind):
> -  ReferenceKind.AddSharedProperty('kind')
> +  Kind.AddSharedProperty('kind')
>  
>    def __init__(self, kind=None):
>      if kind is not None:
> @@ -873,7 +1064,7 @@ class PendingAssociatedRemote(ReferenceKind):
>  
>  
>  class PendingAssociatedReceiver(ReferenceKind):
> -  ReferenceKind.AddSharedProperty('kind')
> +  Kind.AddSharedProperty('kind')
>  
>    def __init__(self, kind=None):
>      if kind is not None:
> @@ -899,7 +1090,7 @@ class PendingAssociatedReceiver(ReferenceKind):
>  
>  
>  class InterfaceRequest(ReferenceKind):
> -  ReferenceKind.AddSharedProperty('kind')
> +  Kind.AddSharedProperty('kind')
>  
>    def __init__(self, kind=None):
>      if kind is not None:
> @@ -923,7 +1114,7 @@ class InterfaceRequest(ReferenceKind):
>  
>  
>  class AssociatedInterfaceRequest(ReferenceKind):
> -  ReferenceKind.AddSharedProperty('kind')
> +  Kind.AddSharedProperty('kind')
>  
>    def __init__(self, kind=None):
>      if kind is not None:
> @@ -949,7 +1140,7 @@ class AssociatedInterfaceRequest(ReferenceKind):
>              self.kind, rhs.kind)
>  
>  
> -class Parameter(object):
> +class Parameter:
>    def __init__(self,
>                 mojom_name=None,
>                 kind=None,
> @@ -983,7 +1174,7 @@ class Parameter(object):
>                                        rhs.default, rhs.attributes))
>  
>  
> -class Method(object):
> +class Method:
>    def __init__(self, interface, mojom_name, ordinal=None, attributes=None):
>      self.interface = interface
>      self.mojom_name = mojom_name
> @@ -999,12 +1190,11 @@ class Method(object):
>    def Repr(self, as_ref=True):
>      if as_ref:
>        return '<%s mojom_name=%r>' % (self.__class__.__name__, self.mojom_name)
> -    else:
> -      return GenericRepr(self, {
> -          'mojom_name': False,
> -          'parameters': True,
> -          'response_parameters': True
> -      })
> +    return GenericRepr(self, {
> +        'mojom_name': False,
> +        'parameters': True,
> +        'response_parameters': True
> +    })
>  
>    def AddParameter(self,
>                     mojom_name,
> @@ -1061,21 +1251,49 @@ class Method(object):
>      return self.attributes.get(ATTRIBUTE_UNLIMITED_SIZE) \
>          if self.attributes else False
>  
> +  @property
> +  def allowed_context(self):
> +    return self.attributes.get(ATTRIBUTE_ALLOWED_CONTEXT) \
> +        if self.attributes else None
> +
> +  @property
> +  def supports_urgent(self):
> +    return self.attributes.get(ATTRIBUTE_SUPPORTS_URGENT) \
> +        if self.attributes else None
> +
> +  @property
> +  def runtime_feature(self):
> +    if not self.attributes:
> +      return None
> +    runtime_feature = self.attributes.get(ATTRIBUTE_RUNTIME_FEATURE, None)
> +    if runtime_feature is None:
> +      return None
> +    if not isinstance(runtime_feature, Feature):
> +      raise Exception("RuntimeFeature attribute on %s must be a feature." %
> +                      self.name)
> +    return runtime_feature
> +
> +  def _tuple(self):
> +    return (self.mojom_name, self.ordinal, self.parameters,
> +            self.response_parameters, self.attributes)
> +
>    def __eq__(self, rhs):
> -    return (isinstance(rhs, Method) and
> -            (self.mojom_name, self.ordinal, self.parameters,
> -             self.response_parameters,
> -             self.attributes) == (rhs.mojom_name, rhs.ordinal, rhs.parameters,
> -                                  rhs.response_parameters, rhs.attributes))
> +    return isinstance(rhs, Method) and self._tuple() == rhs._tuple()
> +
> +  def __lt__(self, rhs):
> +    if not isinstance(self, type(rhs)):
> +      return str(type(self)) < str(type(rhs))
> +
> +    return self._tuple() < rhs._tuple()
>  
>  
>  class Interface(ReferenceKind):
> -  ReferenceKind.AddSharedProperty('mojom_name')
> -  ReferenceKind.AddSharedProperty('name')
> -  ReferenceKind.AddSharedProperty('methods')
> -  ReferenceKind.AddSharedProperty('enums')
> -  ReferenceKind.AddSharedProperty('constants')
> -  ReferenceKind.AddSharedProperty('attributes')
> +  Kind.AddSharedProperty('mojom_name')
> +  Kind.AddSharedProperty('name')
> +  Kind.AddSharedProperty('methods')
> +  Kind.AddSharedProperty('enums')
> +  Kind.AddSharedProperty('constants')
> +  Kind.AddSharedProperty('attributes')
>  
>    def __init__(self, mojom_name=None, module=None, attributes=None):
>      if mojom_name is not None:
> @@ -1093,12 +1311,11 @@ class Interface(ReferenceKind):
>    def Repr(self, as_ref=True):
>      if as_ref:
>        return '<%s mojom_name=%r>' % (self.__class__.__name__, self.mojom_name)
> -    else:
> -      return GenericRepr(self, {
> -          'mojom_name': False,
> -          'attributes': False,
> -          'methods': False
> -      })
> +    return GenericRepr(self, {
> +        'mojom_name': False,
> +        'attributes': False,
> +        'methods': False
> +    })
>  
>    def AddMethod(self, mojom_name, ordinal=None, attributes=None):
>      method = Method(self, mojom_name, ordinal, attributes)
> @@ -1114,10 +1331,10 @@ class Interface(ReferenceKind):
>      for constant in self.constants:
>        constant.Stylize(stylizer)
>  
> -  def IsBackwardCompatible(self, older_interface, checker):
> -    """This interface is backward-compatible with older_interface if and only
> -    if all of the following conditions hold:
> -      - All defined methods in older_interface (when identified by ordinal) have
> +  def IsBackwardCompatible(self, rhs, checker):
> +    """This interface is backward-compatible with rhs (older_interface) if and
> +    only if all of the following conditions hold:
> +      - All defined methods in rhs (when identified by ordinal) have
>          backward-compatible definitions in this interface. For each method this
>          means:
>            - The parameter list is backward-compatible, according to backward-
> @@ -1131,7 +1348,7 @@ class Interface(ReferenceKind):
>              rules for structs.
>        - All newly introduced methods in this interface have a [MinVersion]
>          attribute specifying a version greater than any method in
> -        older_interface.
> +        rhs.
>      """
>  
>      def buildOrdinalMethodMap(interface):
> @@ -1144,7 +1361,7 @@ class Interface(ReferenceKind):
>        return methods_by_ordinal
>  
>      new_methods = buildOrdinalMethodMap(self)
> -    old_methods = buildOrdinalMethodMap(older_interface)
> +    old_methods = buildOrdinalMethodMap(rhs)
>      max_old_min_version = 0
>      for ordinal, old_method in old_methods.items():
>        new_method = new_methods.get(ordinal)
> @@ -1186,6 +1403,39 @@ class Interface(ReferenceKind):
>  
>      return True
>  
> +  @property
> +  def service_sandbox(self):
> +    if not self.attributes:
> +      return None
> +    service_sandbox = self.attributes.get(ATTRIBUTE_SERVICE_SANDBOX, None)
> +    if service_sandbox is None:
> +      return None
> +    # Constants are only allowed to refer to an enum here, so replace.
> +    if isinstance(service_sandbox, Constant):
> +      service_sandbox = service_sandbox.value
> +    if not isinstance(service_sandbox, EnumValue):
> +      raise Exception("ServiceSandbox attribute on %s must be an enum value." %
> +                      self.module.name)
> +    return service_sandbox
> +
> +  @property
> +  def runtime_feature(self):
> +    if not self.attributes:
> +      return None
> +    runtime_feature = self.attributes.get(ATTRIBUTE_RUNTIME_FEATURE, None)
> +    if runtime_feature is None:
> +      return None
> +    if not isinstance(runtime_feature, Feature):
> +      raise Exception("RuntimeFeature attribute on %s must be a feature." %
> +                      self.name)
> +    return runtime_feature
> +
> +  @property
> +  def require_context(self):
> +    if not self.attributes:
> +      return None
> +    return self.attributes.get(ATTRIBUTE_REQUIRE_CONTEXT, None)
> +
>    @property
>    def stable(self):
>      return self.attributes.get(ATTRIBUTE_STABLE, False) \
> @@ -1199,11 +1449,18 @@ class Interface(ReferenceKind):
>        prefix = self.module.GetNamespacePrefix()
>      return '%s%s' % (prefix, self.mojom_name)
>  
> +  def _tuple(self):
> +    return (self.mojom_name, self.methods, self.enums, self.constants,
> +            self.attributes)
> +
>    def __eq__(self, rhs):
> -    return (isinstance(rhs, Interface)
> -            and (self.mojom_name, self.methods, self.enums, self.constants,
> -                 self.attributes) == (rhs.mojom_name, rhs.methods, rhs.enums,
> -                                      rhs.constants, rhs.attributes))
> +    return isinstance(rhs, Interface) and self._tuple() == rhs._tuple()
> +
> +  def __lt__(self, rhs):
> +    if not isinstance(self, type(rhs)):
> +      return str(type(self)) < str(type(rhs))
> +
> +    return self._tuple() < rhs._tuple()
>  
>    @property
>    def uuid(self):
> @@ -1224,7 +1481,7 @@ class Interface(ReferenceKind):
>  
>  
>  class AssociatedInterface(ReferenceKind):
> -  ReferenceKind.AddSharedProperty('kind')
> +  Kind.AddSharedProperty('kind')
>  
>    def __init__(self, kind=None):
>      if kind is not None:
> @@ -1249,7 +1506,7 @@ class AssociatedInterface(ReferenceKind):
>                            self.kind, rhs.kind)
>  
>  
> -class EnumField(object):
> +class EnumField:
>    def __init__(self,
>                 mojom_name=None,
>                 value=None,
> @@ -1281,16 +1538,25 @@ class EnumField(object):
>                                           rhs.attributes, rhs.numeric_value))
>  
>  
> -class Enum(Kind):
> +class Enum(ValueKind):
> +  Kind.AddSharedProperty('mojom_name')
> +  Kind.AddSharedProperty('name')
> +  Kind.AddSharedProperty('native_only')
> +  Kind.AddSharedProperty('fields')
> +  Kind.AddSharedProperty('attributes')
> +  Kind.AddSharedProperty('min_value')
> +  Kind.AddSharedProperty('max_value')
> +  Kind.AddSharedProperty('default_field')
> +
>    def __init__(self, mojom_name=None, module=None, attributes=None):
> -    self.mojom_name = mojom_name
> -    self.name = None
> -    self.native_only = False
>      if mojom_name is not None:
>        spec = 'x:' + mojom_name
>      else:
>        spec = None
> -    Kind.__init__(self, spec, module)
> +    ValueKind.__init__(self, spec, False, module)
> +    self.mojom_name = mojom_name
> +    self.name = None
> +    self.native_only = False
>      self.fields = []
>      self.attributes = attributes
>      self.min_value = None
> @@ -1300,8 +1566,7 @@ class Enum(Kind):
>    def Repr(self, as_ref=True):
>      if as_ref:
>        return '<%s mojom_name=%r>' % (self.__class__.__name__, self.mojom_name)
> -    else:
> -      return GenericRepr(self, {'mojom_name': False, 'fields': False})
> +    return GenericRepr(self, {'mojom_name': False, 'fields': False})
>  
>    def Stylize(self, stylizer):
>      self.name = stylizer.StylizeEnum(self.mojom_name)
> @@ -1327,14 +1592,14 @@ class Enum(Kind):
>      return '%s%s' % (prefix, self.mojom_name)
>  
>    # pylint: disable=unused-argument
> -  def IsBackwardCompatible(self, older_enum, checker):
> -    """This enum is backward-compatible with older_enum if and only if one of
> -    the following conditions holds:
> +  def IsBackwardCompatible(self, rhs, checker):
> +    """This enum is backward-compatible with rhs (older_enum) if and only if one
> +    of the following conditions holds:
>          - Neither enum is [Extensible] and both have the exact same set of valid
>            numeric values. Field names and aliases for the same numeric value do
>            not affect compatibility.
> -        - older_enum is [Extensible], and for every version defined by
> -          older_enum, this enum has the exact same set of valid numeric values.
> +        - rhs is [Extensible], and for every version defined by
> +          rhs, this enum has the exact same set of valid numeric values.
>      """
>  
>      def buildVersionFieldMap(enum):
> @@ -1345,32 +1610,49 @@ class Enum(Kind):
>          fields_by_min_version[field.min_version].add(field.numeric_value)
>        return fields_by_min_version
>  
> -    old_fields = buildVersionFieldMap(older_enum)
> +    old_fields = buildVersionFieldMap(rhs)
>      new_fields = buildVersionFieldMap(self)
>  
> -    if new_fields.keys() != old_fields.keys() and not older_enum.extensible:
> -      return False
> +    if new_fields.keys() != old_fields.keys() and not rhs.extensible:
> +      raise Exception("Non-extensible enum cannot be modified")
>  
>      for min_version, valid_values in old_fields.items():
> -      if (min_version not in new_fields
> -          or new_fields[min_version] != valid_values):
> -        return False
> +      if min_version not in new_fields:
> +        raise Exception('New values added to an extensible enum '
> +                        'do not specify MinVersion: %s' % new_fields)
>  
> +      if (new_fields[min_version] != valid_values):
> +        if (len(new_fields[min_version]) < len(valid_values)):
> +          raise Exception('Removing values for an existing MinVersion %s '
> +                          'is not allowed' % min_version)
> +
> +        raise Exception(
> +            'New values don\'t match old values'
> +            'for an existing MinVersion %s,'
> +            ' please specify MinVersion equal to "Next version" '
> +            'in the enum description'
> +            ' for the following values:\n%s' %
> +            (min_version, new_fields[min_version].difference(valid_values)))
>      return True
>  
> +  def _tuple(self):
> +    return (self.mojom_name, self.native_only, self.fields, self.attributes,
> +            self.min_value, self.max_value, self.default_field)
> +
>    def __eq__(self, rhs):
> -    return (isinstance(rhs, Enum) and
> -            (self.mojom_name, self.native_only, self.fields, self.attributes,
> -             self.min_value, self.max_value,
> -             self.default_field) == (rhs.mojom_name, rhs.native_only,
> -                                     rhs.fields, rhs.attributes, rhs.min_value,
> -                                     rhs.max_value, rhs.default_field))
> +    return isinstance(rhs, Enum) and self._tuple() == rhs._tuple()
> +
> +  def __lt__(self, rhs):
> +    if not isinstance(self, type(rhs)):
> +      return str(type(self)) < str(type(rhs))
> +
> +    return self._tuple() < rhs._tuple()
>  
>    def __hash__(self):
>      return id(self)
>  
>  
> -class Module(object):
> +class Module:
>    def __init__(self, path=None, mojom_namespace=None, attributes=None):
>      self.path = path
>      self.mojom_namespace = mojom_namespace
> @@ -1379,24 +1661,26 @@ class Module(object):
>      self.unions = []
>      self.interfaces = []
>      self.enums = []
> +    self.features = []
>      self.constants = []
> -    self.kinds = {}
> +    self.kinds = OrderedDict()
>      self.attributes = attributes
>      self.imports = []
> -    self.imported_kinds = {}
> -    self.metadata = {}
> +    self.imported_kinds = OrderedDict()
> +    self.metadata = OrderedDict()
>  
>    def __repr__(self):
>      # Gives us a decent __repr__ for modules.
>      return self.Repr()
>  
>    def __eq__(self, rhs):
> -    return (isinstance(rhs, Module) and
> -            (self.path, self.attributes, self.mojom_namespace, self.imports,
> -             self.constants, self.enums, self.structs, self.unions,
> -             self.interfaces) == (rhs.path, rhs.attributes, rhs.mojom_namespace,
> -                                  rhs.imports, rhs.constants, rhs.enums,
> -                                  rhs.structs, rhs.unions, rhs.interfaces))
> +    return (isinstance(rhs, Module)
> +            and (self.path, self.attributes, self.mojom_namespace, self.imports,
> +                 self.constants, self.enums, self.structs, self.unions,
> +                 self.interfaces, self.features)
> +            == (rhs.path, rhs.attributes, rhs.mojom_namespace, rhs.imports,
> +                rhs.constants, rhs.enums, rhs.structs, rhs.unions,
> +                rhs.interfaces, rhs.features))
>  
>    def __hash__(self):
>      return id(self)
> @@ -1405,16 +1689,16 @@ class Module(object):
>      if as_ref:
>        return '<%s path=%r mojom_namespace=%r>' % (
>            self.__class__.__name__, self.path, self.mojom_namespace)
> -    else:
> -      return GenericRepr(
> -          self, {
> -              'path': False,
> -              'mojom_namespace': False,
> -              'attributes': False,
> -              'structs': False,
> -              'interfaces': False,
> -              'unions': False
> -          })
> +    return GenericRepr(
> +        self, {
> +            'path': False,
> +            'mojom_namespace': False,
> +            'attributes': False,
> +            'structs': False,
> +            'interfaces': False,
> +            'unions': False,
> +            'features': False,
> +        })
>  
>    def GetNamespacePrefix(self):
>      return '%s.' % self.mojom_namespace if self.mojom_namespace else ''
> @@ -1434,6 +1718,11 @@ class Module(object):
>      self.unions.append(union)
>      return union
>  
> +  def AddFeature(self, mojom_name, attributes=None):
> +    feature = Feature(mojom_name, self, attributes)
> +    self.features.append(feature)
> +    return feature
> +
>    def Stylize(self, stylizer):
>      self.namespace = stylizer.StylizeModule(self.mojom_namespace)
>      for struct in self.structs:
> @@ -1446,12 +1735,14 @@ class Module(object):
>        enum.Stylize(stylizer)
>      for constant in self.constants:
>        constant.Stylize(stylizer)
> +    for feature in self.features:
> +      feature.Stylize(stylizer)
>  
>      for imported_module in self.imports:
>        imported_module.Stylize(stylizer)
>  
>    def Dump(self, f):
> -    pickle.dump(self, f, 2)
> +    pickle.dump(self, f)
>  
>    @classmethod
>    def Load(cls, f):
> @@ -1461,15 +1752,15 @@ class Module(object):
>  
>  
>  def IsBoolKind(kind):
> -  return kind.spec == BOOL.spec
> +  return kind.spec == BOOL.spec or kind.spec == NULLABLE_BOOL.spec
>  
>  
>  def IsFloatKind(kind):
> -  return kind.spec == FLOAT.spec
> +  return kind.spec == FLOAT.spec or kind.spec == NULLABLE_FLOAT.spec
>  
>  
>  def IsDoubleKind(kind):
> -  return kind.spec == DOUBLE.spec
> +  return kind.spec == DOUBLE.spec or kind.spec == NULLABLE_DOUBLE.spec
>  
>  
>  def IsIntegralKind(kind):
> @@ -1477,7 +1768,14 @@ def IsIntegralKind(kind):
>            or kind.spec == INT16.spec or kind.spec == INT32.spec
>            or kind.spec == INT64.spec or kind.spec == UINT8.spec
>            or kind.spec == UINT16.spec or kind.spec == UINT32.spec
> -          or kind.spec == UINT64.spec)
> +          or kind.spec == UINT64.spec or kind.spec == NULLABLE_BOOL.spec
> +          or kind.spec == NULLABLE_INT8.spec or kind.spec == NULLABLE_INT16.spec
> +          or kind.spec == NULLABLE_INT32.spec
> +          or kind.spec == NULLABLE_INT64.spec
> +          or kind.spec == NULLABLE_UINT8.spec
> +          or kind.spec == NULLABLE_UINT16.spec
> +          or kind.spec == NULLABLE_UINT32.spec
> +          or kind.spec == NULLABLE_UINT64.spec)
>  
>  
>  def IsStringKind(kind):
> @@ -1522,6 +1820,10 @@ def IsArrayKind(kind):
>    return isinstance(kind, Array)
>  
>  
> +def IsFeatureKind(kind):
> +  return isinstance(kind, Feature)
> +
> +
>  def IsInterfaceKind(kind):
>    return isinstance(kind, Interface)
>  
> @@ -1558,12 +1860,16 @@ def IsEnumKind(kind):
>    return isinstance(kind, Enum)
>  
>  
> +def IsValueKind(kind):
> +  return isinstance(kind, ValueKind)
> +
> +
>  def IsReferenceKind(kind):
>    return isinstance(kind, ReferenceKind)
>  
>  
>  def IsNullableKind(kind):
> -  return IsReferenceKind(kind) and kind.is_nullable
> +  return kind.is_nullable
>  
>  
>  def IsMapKind(kind):
> @@ -1664,11 +1970,8 @@ def MethodPassesInterfaces(method):
>    return _AnyMethodParameterRecursive(method, IsInterfaceKind)
>  
>  
> -def HasSyncMethods(interface):
> -  for method in interface.methods:
> -    if method.sync:
> -      return True
> -  return False
> +def GetSyncMethodOrdinals(interface):
> +  return [method.ordinal for method in interface.methods if method.sync]
>  
>  
>  def HasUninterruptableMethods(interface):
> @@ -1700,18 +2003,17 @@ def ContainsHandlesOrInterfaces(kind):
>      checked.add(kind.spec)
>      if IsStructKind(kind):
>        return any(Check(field.kind) for field in kind.fields)
> -    elif IsUnionKind(kind):
> +    if IsUnionKind(kind):
>        return any(Check(field.kind) for field in kind.fields)
> -    elif IsAnyHandleKind(kind):
> +    if IsAnyHandleKind(kind):
>        return True
> -    elif IsAnyInterfaceKind(kind):
> +    if IsAnyInterfaceKind(kind):
>        return True
> -    elif IsArrayKind(kind):
> +    if IsArrayKind(kind):
>        return Check(kind.kind)
> -    elif IsMapKind(kind):
> +    if IsMapKind(kind):
>        return Check(kind.key_kind) or Check(kind.value_kind)
> -    else:
> -      return False
> +    return False
>  
>    return Check(kind)
>  
> @@ -1738,21 +2040,20 @@ def ContainsNativeTypes(kind):
>      checked.add(kind.spec)
>      if IsEnumKind(kind):
>        return kind.native_only
> -    elif IsStructKind(kind):
> +    if IsStructKind(kind):
>        if kind.native_only:
>          return True
>        if any(enum.native_only for enum in kind.enums):
>          return True
>        return any(Check(field.kind) for field in kind.fields)
> -    elif IsUnionKind(kind):
> +    if IsUnionKind(kind):
>        return any(Check(field.kind) for field in kind.fields)
> -    elif IsInterfaceKind(kind):
> +    if IsInterfaceKind(kind):
>        return any(enum.native_only for enum in kind.enums)
> -    elif IsArrayKind(kind):
> +    if IsArrayKind(kind):
>        return Check(kind.kind)
> -    elif IsMapKind(kind):
> +    if IsMapKind(kind):
>        return Check(kind.key_kind) or Check(kind.value_kind)
> -    else:
> -      return False
> +    return False
>  
>    return Check(kind)
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/module_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/module_unittest.py
> index e8fd4936ce82..2a4e852c54d0 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/module_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/module_unittest.py
> @@ -1,4 +1,4 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/pack.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/pack.py
> index 88b77c9887c5..612404260f75 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/pack.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/pack.py
> @@ -1,7 +1,8 @@
> -# Copyright 2013 The Chromium Authors. All rights reserved.
> +# Copyright 2013 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> +import copy
>  from mojom.generate import module as mojom
>  
>  # This module provides a mechanism for determining the packed order and offsets
> @@ -15,7 +16,7 @@ from mojom.generate import module as mojom
>  HEADER_SIZE = 8
>  
>  
> -class PackedField(object):
> +class PackedField:
>    kind_to_size = {
>        mojom.BOOL: 1,
>        mojom.INT8: 1,
> @@ -75,18 +76,55 @@ class PackedField(object):
>        return 8
>      return cls.GetSizeForKind(kind)
>  
> -  def __init__(self, field, index, ordinal):
> +  def __init__(self,
> +               field,
> +               index,
> +               ordinal,
> +               original_field=None,
> +               sub_ordinal=None,
> +               linked_value_packed_field=None):
>      """
>      Args:
>        field: the original field.
>        index: the position of the original field in the struct.
>        ordinal: the ordinal of the field for serialization.
> +      original_field: See below.
> +      sub_ordinal: See below.
> +      linked_value_packed_field: See below.
> +
> +    original_field, sub_ordinal, and linked_value_packed_field are used to
> +    support nullable ValueKind fields. For legacy reasons, nullable ValueKind
> +    fields actually generate two PackedFields. This allows:
> +
> +    - backwards compatibility prior to Mojo support for nullable ValueKinds.
> +    - correct packing of fields for the aforementioned backwards compatibility.
> +
> +    When translating Fields to PackedFields, the original field is turned into
> +    two PackedFields: the first PackedField always has type mojom.BOOL, while
> +    the second PackedField has the non-nullable version of the field's kind.
> +
> +    When constructing these PackedFields, original_field references the field
> +    as defined in the mojom; the name as defined in the mojom will be used for
> +    all layers above the wire/data layer.
> +
> +    sub_ordinal is used to sort the two PackedFields correctly with respect to
> +    each other: the first mojom.BOOL field always has sub_ordinal 0, while the
> +    second field always has sub_ordinal 1.
> +
> +    Finally, linked_value_packed_field is used by the serialization and
> +    deserialization helpers, which generally just iterate over a PackedStruct's
> +    PackedField's in ordinal order. This allows the helpers to easily reference
> +    any related PackedFields rather than having to lookup related PackedFields
> +    by index while iterating.
>      """
>      self.field = field
>      self.index = index
>      self.ordinal = ordinal
> -    self.size = self.GetSizeForKind(field.kind)
> -    self.alignment = self.GetAlignmentForKind(field.kind)
> +    self.original_field = original_field
> +    self.sub_ordinal = sub_ordinal
> +    self.linked_value_packed_field = linked_value_packed_field
> +    self.size = self.GetSizeForKind(self.field.kind)
> +    self.alignment = self.GetAlignmentForKind(self.field.kind)
>      self.offset = None
>      self.bit = None
>      self.min_version = None
> @@ -120,7 +158,33 @@ def GetPayloadSizeUpToField(field):
>    return offset + pad
>  
>  
> -class PackedStruct(object):
> +def IsNullableValueKindPackedField(field):
> +  """Returns true if `field` is derived from a nullable ValueKind field.
> +
> +  Nullable ValueKind fields often require special handling in the bindings due
> +  to the way the implementation is constrained for wire compatibility.
> +  """
> +  assert isinstance(field, PackedField)
> +  return field.sub_ordinal is not None
> +
> +
> +def IsPrimaryNullableValueKindPackedField(field):
> +  """Returns true if `field` is derived from a nullable ValueKind mojom field
> +  and is the "primary" field.
> +
> +  The primary field is a bool PackedField that controls if the field should be
> +  considered as present or not; it will have a reference to the PackedField that
> +  holds the actual value representation if considered present.
> +
> +  Bindings code that translates between the wire protocol and the higher layers
> +  can use this to simplify mapping multiple PackedFields to the single field
> +  that is logically exposed to bindings consumers.
> +  """
> +  assert isinstance(field, PackedField)
> +  return field.linked_value_packed_field is not None
> +
> +
> +class PackedStruct:
>    def __init__(self, struct):
>      self.struct = struct
>      # |packed_fields| contains all the fields, in increasing offset order.
> @@ -139,9 +203,41 @@ class PackedStruct(object):
>      for index, field in enumerate(struct.fields):
>        if field.ordinal is not None:
>          ordinal = field.ordinal
> -      src_fields.append(PackedField(field, index, ordinal))
> +      # Nullable value types are a bit weird: they generate two PackedFields
> +      # despite being a single ValueKind. This is for wire compatibility to
> +      # ease the transition from legacy mojom syntax where nullable value types
> +      # were not supported.
> +      if isinstance(field.kind, mojom.ValueKind) and field.kind.is_nullable:
> +        # The suffixes intentionally use Unicode codepoints which are considered
> +        # valid C++/Java/JavaScript identifiers, yet are unlikely to be used in
> +        # actual user code.
> +        has_value_field = copy.copy(field)
> +        has_value_field.name = f'{field.mojom_name}_$flag'
> +        has_value_field.kind = mojom.BOOL
> +
> +        value_field = copy.copy(field)
> +        value_field.name = f'{field.mojom_name}_$value'
> +        value_field.kind = field.kind.MakeUnnullableKind()
> +
> +        value_packed_field = PackedField(value_field,
> +                                         index,
> +                                         ordinal,
> +                                         original_field=field,
> +                                         sub_ordinal=1,
> +                                         linked_value_packed_field=None)
> +        has_value_packed_field = PackedField(
> +            has_value_field,
> +            index,
> +            ordinal,
> +            original_field=field,
> +            sub_ordinal=0,
> +            linked_value_packed_field=value_packed_field)
> +        src_fields.append(has_value_packed_field)
> +        src_fields.append(value_packed_field)
> +      else:
> +        src_fields.append(PackedField(field, index, ordinal))
>        ordinal += 1
> -    src_fields.sort(key=lambda field: field.ordinal)
> +    src_fields.sort(key=lambda field: (field.ordinal, field.sub_ordinal))
>  
>      # Set |min_version| for each field.
>      next_min_version = 0
> @@ -156,10 +252,11 @@ class PackedStruct(object):
>        if (packed_field.min_version != 0
>            and mojom.IsReferenceKind(packed_field.field.kind)
>            and not packed_field.field.kind.is_nullable):
> -        raise Exception("Non-nullable fields are only allowed in version 0 of "
> -                        "a struct. %s.%s is defined with [MinVersion=%d]." %
> -                        (self.struct.name, packed_field.field.name,
> -                         packed_field.min_version))
> +        raise Exception(
> +            "Non-nullable reference fields are only allowed in version 0 of a "
> +            "struct. %s.%s is defined with [MinVersion=%d]." %
> +            (self.struct.name, packed_field.field.name,
> +             packed_field.min_version))
>  
>      src_field = src_fields[0]
>      src_field.offset = 0
> @@ -186,7 +283,7 @@ class PackedStruct(object):
>          dst_fields.append(src_field)
>  
>  
> -class ByteInfo(object):
> +class ByteInfo:
>    def __init__(self):
>      self.is_padding = False
>      self.packed_fields = []
> @@ -214,10 +311,11 @@ def GetByteLayout(packed_struct):
>    return byte_info
>  
>  
> -class VersionInfo(object):
> -  def __init__(self, version, num_fields, num_bytes):
> +class VersionInfo:
> +  def __init__(self, version, num_fields, num_packed_fields, num_bytes):
>      self.version = version
>      self.num_fields = num_fields
> +    self.num_packed_fields = num_packed_fields
>      self.num_bytes = num_bytes
>  
>  
> @@ -235,24 +333,35 @@ def GetVersionInfo(packed_struct):
>    versions = []
>    last_version = 0
>    last_num_fields = 0
> +  last_num_packed_fields = 0
>    last_payload_size = 0
>  
>    for packed_field in packed_struct.packed_fields_in_ordinal_order:
>      if packed_field.min_version != last_version:
>        versions.append(
> -          VersionInfo(last_version, last_num_fields,
> +          VersionInfo(last_version, last_num_fields, last_num_packed_fields,
>                        last_payload_size + HEADER_SIZE))
>        last_version = packed_field.min_version
>  
> -    last_num_fields += 1
> +    # Nullable numeric fields (e.g. `int32?`) expand to two packed fields, so to
> +    # avoid double-counting, only increment if the field is:
> +    # - not used for representing a nullable value kind field, or
> +    # - the primary field representing the nullable value kind field.
> +    last_num_fields += 1 if (
> +        not IsNullableValueKindPackedField(packed_field)
> +        or IsPrimaryNullableValueKindPackedField(packed_field)) else 0
> +
> +    last_num_packed_fields += 1
> +
>      # The fields are iterated in ordinal order here. However, the size of a
>      # version is determined by the last field of that version in pack order,
>      # instead of ordinal order. Therefore, we need to calculate the max value.
> -    last_payload_size = max(
> -        GetPayloadSizeUpToField(packed_field), last_payload_size)
> +    last_payload_size = max(GetPayloadSizeUpToField(packed_field),
> +                            last_payload_size)
>  
> -  assert len(versions) == 0 or last_num_fields != versions[-1].num_fields
> +  assert len(
> +      versions) == 0 or last_num_packed_fields != versions[-1].num_packed_fields
>    versions.append(
> -      VersionInfo(last_version, last_num_fields,
> +      VersionInfo(last_version, last_num_fields, last_num_packed_fields,
>                    last_payload_size + HEADER_SIZE))
>    return versions
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/pack_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/pack_unittest.py
> index 98c705add32b..7d8e4e019719 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/pack_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/pack_unittest.py
> @@ -1,4 +1,4 @@
> -# Copyright 2013 The Chromium Authors. All rights reserved.
> +# Copyright 2013 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -205,6 +205,34 @@ class PackTest(unittest.TestCase):
>      self.assertEqual(4, versions[2].num_fields)
>      self.assertEqual(32, versions[2].num_bytes)
>  
> +  def testGetVersionInfoPackedStruct(self):
> +    """Tests that pack.GetVersionInfo() correctly sets version, num_fields,
> +    and num_packed_fields for a packed struct.
> +    """
> +    struct = mojom.Struct('test')
> +    struct.AddField('field_0', mojom.BOOL, ordinal=0)
> +    struct.AddField('field_1',
> +                    mojom.NULLABLE_BOOL,
> +                    ordinal=1,
> +                    attributes={'MinVersion': 1})
> +    struct.AddField('field_2',
> +                    mojom.NULLABLE_BOOL,
> +                    ordinal=2,
> +                    attributes={'MinVersion': 2})
> +    ps = pack.PackedStruct(struct)
> +    versions = pack.GetVersionInfo(ps)
> +
> +    self.assertEqual(3, len(versions))
> +    self.assertEqual(0, versions[0].version)
> +    self.assertEqual(1, versions[1].version)
> +    self.assertEqual(2, versions[2].version)
> +    self.assertEqual(1, versions[0].num_fields)
> +    self.assertEqual(2, versions[1].num_fields)
> +    self.assertEqual(3, versions[2].num_fields)
> +    self.assertEqual(1, versions[0].num_packed_fields)
> +    self.assertEqual(3, versions[1].num_packed_fields)
> +    self.assertEqual(5, versions[2].num_packed_fields)
> +
>    def testInterfaceAlignment(self):
>      """Tests that interfaces are aligned on 4-byte boundaries, although the size
>      of an interface is 8 bytes.
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/template_expander.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/template_expander.py
> index 0da900585cea..807e2a4fdfc0 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/template_expander.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/template_expander.py
> @@ -1,4 +1,4 @@
> -# Copyright 2013 The Chromium Authors. All rights reserved.
> +# Copyright 2013 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/translate.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/translate.py
> index 7580b78002e6..83bb297f5d44 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/translate.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/translate.py
> @@ -1,4 +1,4 @@
> -# Copyright 2013 The Chromium Authors. All rights reserved.
> +# Copyright 2013 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Convert parse tree to AST.
> @@ -12,17 +12,294 @@ already been parsed and converted to ASTs before.
>  import itertools
>  import os
>  import re
> -import sys
>  
> +from collections import OrderedDict
>  from mojom.generate import generator
>  from mojom.generate import module as mojom
>  from mojom.parse import ast
>  
>  
> -def _IsStrOrUnicode(x):
> -  if sys.version_info[0] < 3:
> -    return isinstance(x, (unicode, str))
> -  return isinstance(x, str)
> +is_running_backwards_compatibility_check_hack = False
> +
> +### DO NOT ADD ENTRIES TO THIS LIST. ###
> +_EXTENSIBLE_ENUMS_MISSING_DEFAULT = (
> +    'x:arc.keymaster.mojom.Algorithm',
> +    'x:arc.keymaster.mojom.Digest',
> +    'x:arc.keymaster.mojom.SignatureResult',
> +    'x:arc.mojom.AccessibilityActionType',
> +    'x:arc.mojom.AccessibilityBooleanProperty',
> +    'x:arc.mojom.AccessibilityEventIntListProperty',
> +    'x:arc.mojom.AccessibilityEventIntProperty',
> +    'x:arc.mojom.AccessibilityEventStringProperty',
> +    'x:arc.mojom.AccessibilityEventType',
> +    'x:arc.mojom.AccessibilityFilterType',
> +    'x:arc.mojom.AccessibilityIntListProperty',
> +    'x:arc.mojom.AccessibilityIntProperty',
> +    'x:arc.mojom.AccessibilityLiveRegionType',
> +    'x:arc.mojom.AccessibilityNotificationStateType',
> +    'x:arc.mojom.AccessibilityRangeType',
> +    'x:arc.mojom.AccessibilitySelectionMode',
> +    'x:arc.mojom.AccessibilityStringListProperty',
> +    'x:arc.mojom.AccessibilityStringProperty',
> +    'x:arc.mojom.AccessibilityWindowBooleanProperty',
> +    'x:arc.mojom.AccessibilityWindowIntListProperty',
> +    'x:arc.mojom.AccessibilityWindowIntProperty',
> +    'x:arc.mojom.AccessibilityWindowStringProperty',
> +    'x:arc.mojom.AccessibilityWindowType',
> +    'x:arc.mojom.AccountCheckStatus',
> +    'x:arc.mojom.AccountUpdateType',
> +    'x:arc.mojom.ActionType',
> +    'x:arc.mojom.Algorithm',
> +    'x:arc.mojom.AndroidIdSource',
> +    'x:arc.mojom.AnrSource',
> +    'x:arc.mojom.AnrType',
> +    'x:arc.mojom.AppDiscoveryRequestState',
> +    'x:arc.mojom.AppKillType',
> +    'x:arc.mojom.AppPermission',
> +    'x:arc.mojom.AppPermissionGroup',
> +    'x:arc.mojom.AppReinstallState',
> +    'x:arc.mojom.AppShortcutItemType',
> +    'x:arc.mojom.ArcAuthCodeStatus',
> +    'x:arc.mojom.ArcClipboardDragDropEvent',
> +    'x:arc.mojom.ArcCorePriAbiMigEvent',
> +    'x:arc.mojom.ArcDnsQuery',
> +    'x:arc.mojom.ArcImageCopyPasteCompatAction',
> +    'x:arc.mojom.ArcNetworkError',
> +    'x:arc.mojom.ArcNetworkEvent',
> +    'x:arc.mojom.ArcNotificationEvent',
> +    'x:arc.mojom.ArcNotificationExpandState',
> +    'x:arc.mojom.ArcNotificationPriority',
> +    'x:arc.mojom.ArcNotificationRemoteInputState',
> +    'x:arc.mojom.ArcNotificationShownContents',
> +    'x:arc.mojom.ArcNotificationStyle',
> +    'x:arc.mojom.ArcNotificationType',
> +    'x:arc.mojom.ArcPipEvent',
> +    'x:arc.mojom.ArcResizeLockState',
> +    'x:arc.mojom.ArcSignInSuccess',
> +    'x:arc.mojom.ArcTimerResult',
> +    'x:arc.mojom.AudioSwitch',
> +    'x:arc.mojom.BluetoothAclState',
> +    'x:arc.mojom.BluetoothAdapterState',
> +    'x:arc.mojom.BluetoothAdvertisingDataType',
> +    'x:arc.mojom.BluetoothBondState',
> +    'x:arc.mojom.BluetoothDeviceType',
> +    'x:arc.mojom.BluetoothDiscoveryState',
> +    'x:arc.mojom.BluetoothGattDBAttributeType',
> +    'x:arc.mojom.BluetoothGattStatus',
> +    'x:arc.mojom.BluetoothPropertyType',
> +    'x:arc.mojom.BluetoothScanMode',
> +    'x:arc.mojom.BluetoothSdpAttributeType',
> +    'x:arc.mojom.BluetoothSocketType',
> +    'x:arc.mojom.BluetoothStatus',
> +    'x:arc.mojom.BootType',
> +    'x:arc.mojom.CaptionTextShadowType',
> +    'x:arc.mojom.ChangeType',
> +    'x:arc.mojom.ChromeAccountType',
> +    'x:arc.mojom.ChromeApp',
> +    'x:arc.mojom.ChromePage',
> +    'x:arc.mojom.ClockId',
> +    'x:arc.mojom.CloudProvisionFlowError',
> +    'x:arc.mojom.CommandResultType',
> +    'x:arc.mojom.CompanionLibApiId',
> +    'x:arc.mojom.ConnectionStateType',
> +    'x:arc.mojom.ContentChangeType',
> +    'x:arc.mojom.CpuRestrictionState',
> +    'x:arc.mojom.CursorCoordinateSpace',
> +    'x:arc.mojom.DataRestoreStatus',
> +    'x:arc.mojom.DecoderStatus',
> +    'x:arc.mojom.DeviceType',
> +    'x:arc.mojom.Digest',
> +    'x:arc.mojom.DisplayWakeLockType',
> +    'x:arc.mojom.EapMethod',
> +    'x:arc.mojom.EapPhase2Method',
> +    'x:arc.mojom.FileSelectorEventType',
> +    'x:arc.mojom.GMSCheckInError',
> +    'x:arc.mojom.GMSSignInError',
> +    'x:arc.mojom.GeneralSignInError',
> +    'x:arc.mojom.GetNetworksRequestType',
> +    'x:arc.mojom.HalPixelFormat',
> +    'x:arc.mojom.IPAddressType',
> +    'x:arc.mojom.InstallErrorReason',
> +    'x:arc.mojom.KeyFormat',
> +    'x:arc.mojom.KeyManagement',
> +    'x:arc.mojom.KeyPurpose',
> +    'x:arc.mojom.KeymasterError',
> +    'x:arc.mojom.MainAccountHashMigrationStatus',
> +    'x:arc.mojom.MainAccountResolutionStatus',
> +    'x:arc.mojom.ManagementChangeStatus',
> +    'x:arc.mojom.ManagementState',
> +    'x:arc.mojom.MessageCenterVisibility',
> +    'x:arc.mojom.MetricsType',
> +    'x:arc.mojom.MountEvent',
> +    'x:arc.mojom.NativeBridgeType',
> +    'x:arc.mojom.NetworkResult',
> +    'x:arc.mojom.NetworkType',
> +    'x:arc.mojom.OemCryptoAlgorithm',
> +    'x:arc.mojom.OemCryptoCipherMode',
> +    'x:arc.mojom.OemCryptoHdcpCapability',
> +    'x:arc.mojom.OemCryptoLicenseType',
> +    'x:arc.mojom.OemCryptoPrivateKey',
> +    'x:arc.mojom.OemCryptoProvisioningMethod',
> +    'x:arc.mojom.OemCryptoResult',
> +    'x:arc.mojom.OemCryptoRsaPaddingScheme',
> +    'x:arc.mojom.OemCryptoUsageEntryStatus',
> +    'x:arc.mojom.Padding',
> +    'x:arc.mojom.PaiFlowState',
> +    'x:arc.mojom.PatternType',
> +    'x:arc.mojom.PressureLevel',
> +    'x:arc.mojom.PrintColorMode',
> +    'x:arc.mojom.PrintContentType',
> +    'x:arc.mojom.PrintDuplexMode',
> +    'x:arc.mojom.PrinterStatus',
> +    'x:arc.mojom.ProcessState',
> +    'x:arc.mojom.PurchaseState',
> +    'x:arc.mojom.ReauthReason',
> +    'x:arc.mojom.ScaleFactor',
> +    'x:arc.mojom.SecurityType',
> +    'x:arc.mojom.SegmentStyle',
> +    'x:arc.mojom.SelectFilesActionType',
> +    'x:arc.mojom.SetNativeChromeVoxResponse',
> +    'x:arc.mojom.ShowPackageInfoPage',
> +    'x:arc.mojom.SpanType',
> +    'x:arc.mojom.SupportedLinkChangeSource',
> +    'x:arc.mojom.TetheringClientState',
> +    'x:arc.mojom.TextInputType',
> +    'x:arc.mojom.TtsEventType',
> +    'x:arc.mojom.VideoCodecProfile',
> +    'x:arc.mojom.VideoDecodeAccelerator.Result',
> +    'x:arc.mojom.VideoEncodeAccelerator.Error',
> +    'x:arc.mojom.VideoFrameStorageType',
> +    'x:arc.mojom.VideoPixelFormat',
> +    'x:arc.mojom.WakefulnessMode',
> +    'x:arc.mojom.WebApkInstallResult',
> +    'x:ash.ime.mojom.InputFieldType',
> +    'x:ash.ime.mojom.PersonalizationMode',
> +    'x:ash.language.mojom.FeatureId',
> +    'x:blink.mojom.ScrollRestorationType',
> +    'x:chromeos.cdm.mojom.CdmKeyStatus',
> +    'x:chromeos.cdm.mojom.CdmMessageType',
> +    'x:chromeos.cdm.mojom.CdmSessionType',
> +    'x:chromeos.cdm.mojom.DecryptStatus',
> +    'x:chromeos.cdm.mojom.EmeInitDataType',
> +    'x:chromeos.cdm.mojom.EncryptionScheme',
> +    'x:chromeos.cdm.mojom.HdcpVersion',
> +    'x:chromeos.cdm.mojom.OutputProtection.LinkType',
> +    'x:chromeos.cdm.mojom.OutputProtection.ProtectionType',
> +    'x:chromeos.cdm.mojom.PromiseException',
> +    'x:chromeos.cfm.mojom.EnqueuePriority',
> +    'x:chromeos.cfm.mojom.LoggerErrorCode',
> +    'x:chromeos.cfm.mojom.LoggerState',
> +    'x:chromeos.cros_healthd.mojom.CryptoAlgorithm',
> +    'x:chromeos.cros_healthd.mojom.EncryptionState',
> +    'x:chromeos.machine_learning.mojom.AnnotationUsecase',
> +    'x:chromeos.machine_learning.mojom.BuiltinModelId',
> +    'x:chromeos.machine_learning.mojom.CreateGraphExecutorResult',
> +    'x:chromeos.machine_learning.mojom.DocumentScannerResultStatus',
> +    'x:chromeos.machine_learning.mojom.EndpointReason',
> +    'x:chromeos.machine_learning.mojom.EndpointerType',
> +    'x:chromeos.machine_learning.mojom.ExecuteResult',
> +    'x:chromeos.machine_learning.mojom.GrammarCheckerResult.Status',
> +    'x:chromeos.machine_learning.mojom.HandwritingRecognizerResult.Status',
> +    'x:chromeos.machine_learning.mojom.LoadHandwritingModelResult',
> +    'x:chromeos.machine_learning.mojom.LoadModelResult',
> +    'x:chromeos.machine_learning.mojom.Rotation',
> +    'x:chromeos.network_config.mojom.ConnectionStateType',
> +    'x:chromeos.network_config.mojom.DeviceStateType',
> +    'x:chromeos.network_config.mojom.IPConfigType',
> +    'x:chromeos.network_config.mojom.NetworkType',
> +    'x:chromeos.network_config.mojom.OncSource',
> +    'x:chromeos.network_config.mojom.PolicySource',
> +    'x:chromeos.network_config.mojom.PortalState',
> +    'x:chromeos.wilco_dtc_supportd.mojom.WilcoDtcSupportdEvent',
> +    'x:chromeos.wilco_dtc_supportd.mojom.WilcoDtcSupportdWebRequestHttpMethod',
> +    'x:chromeos.wilco_dtc_supportd.mojom.WilcoDtcSupportdWebRequestStatus',
> +    'x:cros.mojom.CameraClientType',
> +    'x:cros.mojom.CameraMetadataSectionStart',
> +    'x:cros.mojom.CameraMetadataTag',
> +    'x:cros.mojom.HalPixelFormat',
> +    'x:crosapi.mojom.AllowedPaths',
> +    'x:crosapi.mojom.BrowserAppInstanceType',
> +    'x:crosapi.mojom.CreationResult',
> +    'x:crosapi.mojom.DeviceAccessResultCode',
> +    'x:crosapi.mojom.DeviceMode',
> +    'x:crosapi.mojom.DlpRestrictionLevel',
> +    'x:crosapi.mojom.ExoImeSupport',
> +    'x:crosapi.mojom.FullscreenVisibility',
> +    'x:crosapi.mojom.GoogleServiceAuthError.State',
> +    'x:crosapi.mojom.IsInstallableResult',
> +    'x:crosapi.mojom.KeyTag',
> +    'x:crosapi.mojom.KeystoreSigningAlgorithmName',
> +    'x:crosapi.mojom.KeystoreType',
> +    'x:crosapi.mojom.LacrosFeedbackSource',
> +    'x:crosapi.mojom.MemoryPressureLevel',
> +    'x:crosapi.mojom.MetricsReportingManaged',
> +    'x:crosapi.mojom.NotificationType',
> +    'x:crosapi.mojom.OndeviceHandwritingSupport',
> +    'x:crosapi.mojom.OpenResult',
> +    'x:crosapi.mojom.PolicyDomain',
> +    'x:crosapi.mojom.RegistrationCodeType',
> +    'x:crosapi.mojom.ScaleFactor',
> +    'x:crosapi.mojom.SearchResult.OptionalBool',
> +    'x:crosapi.mojom.SelectFileDialogType',
> +    'x:crosapi.mojom.SelectFileResult',
> +    'x:crosapi.mojom.SharesheetResult',
> +    'x:crosapi.mojom.TouchEventType',
> +    'x:crosapi.mojom.VideoRotation',
> +    'x:crosapi.mojom.WallpaperLayout',
> +    'x:crosapi.mojom.WebAppInstallResultCode',
> +    'x:crosapi.mojom.WebAppUninstallResultCode',
> +    'x:device.mojom.HidBusType',
> +    'x:device.mojom.WakeLockReason',
> +    'x:device.mojom.WakeLockType',
> +    'x:drivefs.mojom.DialogReason.Type',
> +    'x:drivefs.mojom.DriveError.Type',
> +    'x:drivefs.mojom.DriveFsDelegate.ExtensionConnectionStatus',
> +    'x:drivefs.mojom.FileMetadata.CanPinStatus',
> +    'x:drivefs.mojom.FileMetadata.Type',
> +    'x:drivefs.mojom.ItemEventReason',
> +    'x:drivefs.mojom.MirrorPathStatus',
> +    'x:drivefs.mojom.MirrorSyncStatus',
> +    'x:drivefs.mojom.QueryParameters.SortField',
> +    'x:fuzz.mojom.FuzzEnum',
> +    'x:media.mojom.FillLightMode',
> +    'x:media.mojom.MeteringMode',
> +    'x:media.mojom.PowerLineFrequency',
> +    'x:media.mojom.RedEyeReduction',
> +    'x:media.mojom.ResolutionChangePolicy',
> +    'x:media.mojom.VideoCaptureApi',
> +    'x:media.mojom.VideoCaptureBufferType',
> +    'x:media.mojom.VideoCaptureError',
> +    'x:media.mojom.VideoCaptureFrameDropReason',
> +    'x:media.mojom.VideoCapturePixelFormat',
> +    'x:media.mojom.VideoCaptureTransportType',
> +    'x:media.mojom.VideoFacingMode',
> +    'x:media_session.mojom.AudioFocusType',
> +    'x:media_session.mojom.CameraState',
> +    'x:media_session.mojom.EnforcementMode',
> +    'x:media_session.mojom.MediaAudioVideoState',
> +    'x:media_session.mojom.MediaImageBitmapColorType',
> +    'x:media_session.mojom.MediaPictureInPictureState',
> +    'x:media_session.mojom.MediaPlaybackState',
> +    'x:media_session.mojom.MediaSession.SuspendType',
> +    'x:media_session.mojom.MediaSessionAction',
> +    'x:media_session.mojom.MediaSessionImageType',
> +    'x:media_session.mojom.MediaSessionInfo.SessionState',
> +    'x:media_session.mojom.MicrophoneState',
> +    'x:ml.model_loader.mojom.ComputeResult',
> +    'x:ml.model_loader.mojom.CreateModelLoaderResult',
> +    'x:ml.model_loader.mojom.LoadModelResult',
> +    'x:mojo.test.AnExtensibleEnum',
> +    'x:mojo.test.EnumB',
> +    'x:mojo.test.ExtensibleEmptyEnum',
> +    'x:mojo.test.enum_default_unittest.mojom.ExtensibleEnumWithoutDefault',
> +    'x:network.mojom.WebSandboxFlags',
> +    'x:payments.mojom.BillingResponseCode',
> +    'x:payments.mojom.CreateDigitalGoodsResponseCode',
> +    'x:payments.mojom.ItemType',
> +    'x:printing.mojom.PrinterType',
> +    'x:ui.mojom.KeyboardCode',
> +)
> +### DO NOT ADD ENTRIES TO THIS LIST. ###
>  
>  
>  def _DuplicateName(values):
> @@ -98,12 +375,6 @@ def _MapKind(kind):
>    }
>    if kind.endswith('?'):
>      base_kind = _MapKind(kind[0:-1])
> -    # NOTE: This doesn't rule out enum types. Those will be detected later, when
> -    # cross-reference is established.
> -    reference_kinds = ('m', 's', 'h', 'a', 'r', 'x', 'asso', 'rmt', 'rcv',
> -                       'rma', 'rca')
> -    if re.split('[^a-z]', base_kind, 1)[0] not in reference_kinds:
> -      raise Exception('A type (spec "%s") cannot be made nullable' % base_kind)
>      return '?' + base_kind
>    if kind.endswith('}'):
>      lbracket = kind.rfind('{')
> @@ -113,8 +384,6 @@ def _MapKind(kind):
>      lbracket = kind.rfind('[')
>      typename = kind[0:lbracket]
>      return 'a' + kind[lbracket + 1:-1] + ':' + _MapKind(typename)
> -  if kind.endswith('&'):
> -    return 'r:' + _MapKind(kind[0:-1])
>    if kind.startswith('asso<'):
>      assert kind.endswith('>')
>      return 'asso:' + _MapKind(kind[5:-1])
> @@ -135,13 +404,45 @@ def _MapKind(kind):
>    return 'x:' + kind
>  
>  
> -def _AttributeListToDict(attribute_list):
> +def _MapAttributeValue(module, kind, value):
> +  # True/False/None
> +  if value is None:
> +    return value
> +  if not isinstance(value, str):
> +    return value
> +  # Is the attribute value the name of a feature?
> +  try:
> +    # Features cannot be nested in other types, so lookup in the global scope.
> +    trial = _LookupKind(module.kinds, 'x:' + value,
> +                        _GetScopeForKind(module, kind))
> +    if isinstance(trial, mojom.Feature):
> +      return trial
> +  except ValueError:
> +    pass
> +  # Is the attribute value a constant or enum value?
> +  try:
> +    trial = _LookupValue(module, None, None, ('IDENTIFIER', value))
> +    if isinstance(trial, mojom.ConstantValue):
> +      return trial.constant
> +    if isinstance(trial, mojom.EnumValue):
> +      return trial
> +  except ValueError:
> +    pass
> +  # If not a referenceable mojo type - return as a string.
> +  return value
> +
> +
> +def _AttributeListToDict(module, kind, attribute_list):
>    if attribute_list is None:
>      return None
>    assert isinstance(attribute_list, ast.AttributeList)
> -  # TODO(vtl): Check for duplicate keys here.
> -  return dict(
> -      [(attribute.key, attribute.value) for attribute in attribute_list])
> +  attributes = dict()
> +  for attribute in attribute_list:
> +    if attribute.key in attributes:
> +      raise Exception("Duplicate key (%s) in attribute list" % attribute.key)
> +    attributes[attribute.key] = _MapAttributeValue(module, kind,
> +                                                   attribute.value)
> +  return attributes
>  
>  
>  builtin_values = frozenset([
> @@ -257,7 +558,8 @@ def _Kind(kinds, spec, scope):
>      return kind
>  
>    if spec.startswith('?'):
> -    kind = _Kind(kinds, spec[1:], scope).MakeNullableKind()
> +    kind = _Kind(kinds, spec[1:], scope)
> +    kind = kind.MakeNullableKind()
>    elif spec.startswith('a:'):
>      kind = mojom.Array(_Kind(kinds, spec[2:], scope))
>    elif spec.startswith('asso:'):
> @@ -303,7 +605,8 @@ def _Kind(kinds, spec, scope):
>  
>  def _Import(module, import_module):
>    # Copy the struct kinds from our imports into the current module.
> -  importable_kinds = (mojom.Struct, mojom.Union, mojom.Enum, mojom.Interface)
> +  importable_kinds = (mojom.Struct, mojom.Union, mojom.Enum, mojom.Interface,
> +                      mojom.Feature)
>    for kind in import_module.kinds.values():
>      if (isinstance(kind, importable_kinds)
>          and kind.module.path == import_module.path):
> @@ -316,6 +619,32 @@ def _Import(module, import_module):
>    return import_module
>  
>  
> +def _Feature(module, parsed_feature):
> +  """
> +  Args:
> +    module: {mojom.Module} Module currently being constructed.
> +    parsed_feature: {ast.Feature} Parsed feature.
> +
> +  Returns:
> +    {mojom.Feature} AST feature.
> +  """
> +  feature = mojom.Feature(module=module)
> +  feature.mojom_name = parsed_feature.mojom_name
> +  feature.spec = 'x:' + module.GetNamespacePrefix() + feature.mojom_name
> +  module.kinds[feature.spec] = feature
> +  feature.constants = []
> +  _ProcessElements(
> +      parsed_feature.mojom_name, parsed_feature.body, {
> +          ast.Const:
> +          lambda const: feature.constants.append(
> +              _Constant(module, const, feature)),
> +      })
> +
> +  feature.attributes = _AttributeListToDict(module, feature,
> +                                            parsed_feature.attribute_list)
> +  return feature
> +
> +
>  def _Struct(module, parsed_struct):
>    """
>    Args:
> @@ -345,7 +674,8 @@ def _Struct(module, parsed_struct):
>              struct.fields_data.append,
>          })
>  
> -  struct.attributes = _AttributeListToDict(parsed_struct.attribute_list)
> +  struct.attributes = _AttributeListToDict(module, struct,
> +                                           parsed_struct.attribute_list)
>  
>    # Enforce that a [Native] attribute is set to make native-only struct
>    # declarations more explicit.
> @@ -377,7 +707,8 @@ def _Union(module, parsed_union):
>    union.fields_data = []
>    _ProcessElements(parsed_union.mojom_name, parsed_union.body,
>                     {ast.UnionField: union.fields_data.append})
> -  union.attributes = _AttributeListToDict(parsed_union.attribute_list)
> +  union.attributes = _AttributeListToDict(module, union,
> +                                          parsed_union.attribute_list)
>    return union
>  
>  
> @@ -398,7 +729,8 @@ def _StructField(module, parsed_field, struct):
>    field.ordinal = parsed_field.ordinal.value if parsed_field.ordinal else None
>    field.default = _LookupValue(module, struct, field.kind,
>                                 parsed_field.default_value)
> -  field.attributes = _AttributeListToDict(parsed_field.attribute_list)
> +  field.attributes = _AttributeListToDict(module, field,
> +                                          parsed_field.attribute_list)
>    return field
>  
>  
> @@ -414,11 +746,22 @@ def _UnionField(module, parsed_field, union):
>    """
>    field = mojom.UnionField()
>    field.mojom_name = parsed_field.mojom_name
> +  # Disallow unions from being self-recursive.
> +  parsed_typename = parsed_field.typename
> +  if parsed_typename.endswith('?'):
> +    parsed_typename = parsed_typename[:-1]
> +  assert parsed_typename != union.mojom_name
>    field.kind = _Kind(module.kinds, _MapKind(parsed_field.typename),
>                       (module.mojom_namespace, union.mojom_name))
>    field.ordinal = parsed_field.ordinal.value if parsed_field.ordinal else None
>    field.default = None
> -  field.attributes = _AttributeListToDict(parsed_field.attribute_list)
> +  field.attributes = _AttributeListToDict(module, field,
> +                                          parsed_field.attribute_list)
> +  if field.is_default and not mojom.IsNullableKind(field.kind) and \
> +     not mojom.IsIntegralKind(field.kind):
> +    raise Exception(
> +        '[Default] field for union %s must be nullable or integral type.' %
> +        union.mojom_name)
>    return field
>  
>  
> @@ -439,7 +782,8 @@ def _Parameter(module, parsed_param, interface):
>    parameter.ordinal = (parsed_param.ordinal.value
>                         if parsed_param.ordinal else None)
>    parameter.default = None  # TODO(tibell): We never have these. Remove field?
> -  parameter.attributes = _AttributeListToDict(parsed_param.attribute_list)
> +  parameter.attributes = _AttributeListToDict(module, parameter,
> +                                              parsed_param.attribute_list)
>    return parameter
>  
>  
> @@ -464,7 +808,8 @@ def _Method(module, parsed_method, interface):
>      method.response_parameters = list(
>          map(lambda parameter: _Parameter(module, parameter, interface),
>              parsed_method.response_parameter_list))
> -  method.attributes = _AttributeListToDict(parsed_method.attribute_list)
> +  method.attributes = _AttributeListToDict(module, method,
> +                                           parsed_method.attribute_list)
>  
>    # Enforce that only methods with response can have a [Sync] attribute.
>    if method.sync and method.response_parameters is None:
> @@ -492,7 +837,8 @@ def _Interface(module, parsed_iface):
>    interface.mojom_name = parsed_iface.mojom_name
>    interface.spec = 'x:' + module.GetNamespacePrefix() + interface.mojom_name
>    module.kinds[interface.spec] = interface
> -  interface.attributes = _AttributeListToDict(parsed_iface.attribute_list)
> +  interface.attributes = _AttributeListToDict(module, interface,
> +                                              parsed_iface.attribute_list)
>    interface.enums = []
>    interface.constants = []
>    interface.methods_data = []
> @@ -522,7 +868,8 @@ def _EnumField(module, enum, parsed_field):
>    field = mojom.EnumField()
>    field.mojom_name = parsed_field.mojom_name
>    field.value = _LookupValue(module, enum, None, parsed_field.value)
> -  field.attributes = _AttributeListToDict(parsed_field.attribute_list)
> +  field.attributes = _AttributeListToDict(module, field,
> +                                          parsed_field.attribute_list)
>    value = mojom.EnumValue(module, enum, field)
>    module.values[value.GetSpec()] = value
>    return field
> @@ -544,7 +891,7 @@ def _ResolveNumericEnumValues(enum):
>        prev_value += 1
>  
>      # Integral value (e.g: BEGIN = -0x1).
> -    elif _IsStrOrUnicode(field.value):
> +    elif isinstance(field.value, str):
>        prev_value = int(field.value, 0)
>  
>      # Reference to a previous enum value (e.g: INIT = BEGIN).
> @@ -560,7 +907,10 @@ def _ResolveNumericEnumValues(enum):
>      else:
>        raise Exception('Unresolved enum value for %s' % field.value.GetSpec())
>  
> -    #resolved_enum_values[field.mojom_name] = prev_value
> +    if prev_value in (-128, -127):
> +      raise Exception(f'{field.mojom_name} in {enum.spec} has the value '
> +                      f'{prev_value}, which is reserved for WTF::HashTrait\'s '
> +                      'default enum specialization and may not be used.')
>      field.numeric_value = prev_value
>      if min_value is None or prev_value < min_value:
>        min_value = prev_value
> @@ -588,7 +938,8 @@ def _Enum(module, parsed_enum, parent_kind):
>      mojom_name = parent_kind.mojom_name + '.' + mojom_name
>    enum.spec = 'x:%s.%s' % (module.mojom_namespace, mojom_name)
>    enum.parent_kind = parent_kind
> -  enum.attributes = _AttributeListToDict(parsed_enum.attribute_list)
> +  enum.attributes = _AttributeListToDict(module, enum,
> +                                         parsed_enum.attribute_list)
>  
>    if not enum.native_only:
>      enum.fields = list(
> @@ -600,11 +951,18 @@ def _Enum(module, parsed_enum, parent_kind):
>      for field in enum.fields:
>        if field.default:
>          if not enum.extensible:
> -          raise Exception('Non-extensible enums may not specify a default')
> -        if enum.default_field is not None:
>            raise Exception(
> -              'Only one enumerator value may be specified as the default')
> +              f'Non-extensible enum {enum.spec} may not specify a default')
> +        if enum.default_field is not None:
> +          raise Exception(f'Multiple [Default] enumerators in enum {enum.spec}')
>          enum.default_field = field
> +    # While running the backwards compatibility check, ignore errors because the
> +    # old version of the enum might not specify [Default].
> +    if (enum.extensible and enum.default_field is None
> +        and enum.spec not in _EXTENSIBLE_ENUMS_MISSING_DEFAULT
> +        and not is_running_backwards_compatibility_check_hack):
> +      raise Exception(
> +          f'Extensible enum {enum.spec} must specify a [Default] enumerator')
>  
>    module.kinds[enum.spec] = enum
>  
> @@ -696,6 +1054,11 @@ def _CollectReferencedKinds(module, all_defined_kinds):
>          for referenced_kind in extract_referenced_user_kinds(param.kind):
>            sanitized_kind = sanitize_kind(referenced_kind)
>            referenced_user_kinds[sanitized_kind.spec] = sanitized_kind
> +  # Consts can reference imported enums.
> +  for const in module.constants:
> +    if not const.kind in mojom.PRIMITIVES:
> +      sanitized_kind = sanitize_kind(const.kind)
> +      referenced_user_kinds[sanitized_kind.spec] = sanitized_kind
>  
>    return referenced_user_kinds
>  
> @@ -741,6 +1104,16 @@ def _AssertTypeIsStable(kind):
>            assertDependencyIsStable(response_param.kind)
>  
>  
> +def _AssertStructIsValid(kind):
> +  expected_ordinals = set(range(0, len(kind.fields)))
> +  ordinals = set(map(lambda field: field.ordinal, kind.fields))
> +  if ordinals != expected_ordinals:
> +    raise Exception(
> +        'Structs must use contiguous ordinals starting from 0. ' +
> +        '{} is missing the following ordinals: {}.'.format(
> +            kind.mojom_name, ', '.join(map(str, expected_ordinals - ordinals))))
> +
> +
>  def _Module(tree, path, imports):
>    """
>    Args:
> @@ -778,6 +1151,8 @@ def _Module(tree, path, imports):
>    module.structs = []
>    module.unions = []
>    module.interfaces = []
> +  module.features = []
> +
>    _ProcessElements(
>        filename, tree.definition_list, {
>            ast.Const:
> @@ -791,6 +1166,8 @@ def _Module(tree, path, imports):
>            ast.Interface:
>            lambda interface: module.interfaces.append(
>                _Interface(module, interface)),
> +          ast.Feature:
> +          lambda feature: module.features.append(_Feature(module, feature)),
>        })
>  
>    # Second pass expands fields and methods. This allows fields and parameters
> @@ -806,12 +1183,24 @@ def _Module(tree, path, imports):
>      for enum in struct.enums:
>        all_defined_kinds[enum.spec] = enum
>  
> +  for feature in module.features:
> +    all_defined_kinds[feature.spec] = feature
> +
>    for union in module.unions:
>      union.fields = list(
>          map(lambda field: _UnionField(module, field, union), union.fields_data))
>      _AssignDefaultOrdinals(union.fields)
> +    for field in union.fields:
> +      if field.is_default:
> +        if union.default_field is not None:
> +          raise Exception('Multiple [Default] fields in union %s.' %
> +                          union.mojom_name)
> +        union.default_field = field
>      del union.fields_data
>      all_defined_kinds[union.spec] = union
> +    if union.extensible and union.default_field is None:
> +      raise Exception('Extensible union %s must specify a [Default] field' %
> +                      union.mojom_name)
>  
>    for interface in module.interfaces:
>      interface.methods = list(
> @@ -829,8 +1218,8 @@ def _Module(tree, path, imports):
>                                                   all_defined_kinds.values())
>    imported_kind_specs = set(all_referenced_kinds.keys()).difference(
>        set(all_defined_kinds.keys()))
> -  module.imported_kinds = dict(
> -      (spec, all_referenced_kinds[spec]) for spec in imported_kind_specs)
> +  module.imported_kinds = OrderedDict((spec, all_referenced_kinds[spec])
> +                                      for spec in sorted(imported_kind_specs))
>  
>    generator.AddComputedData(module)
>    for iface in module.interfaces:
> @@ -847,6 +1236,9 @@ def _Module(tree, path, imports):
>        if kind.stable:
>          _AssertTypeIsStable(kind)
>  
> +  for kind in module.structs:
> +    _AssertStructIsValid(kind)
> +
>    return module
>  
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/generate/translate_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/generate/translate_unittest.py
> index 19905c8a9540..b4fea92467d5 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/generate/translate_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/generate/translate_unittest.py
> @@ -1,17 +1,13 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import imp
> -import os.path
> -import sys
>  import unittest
>  
>  from mojom.generate import module as mojom
>  from mojom.generate import translate
>  from mojom.parse import ast
>  
> -
>  class TranslateTest(unittest.TestCase):
>    """Tests |parser.Parse()|."""
>  
> @@ -69,5 +65,77 @@ class TranslateTest(unittest.TestCase):
>      # pylint: disable=W0212
>      self.assertEquals(
>          translate._MapKind("asso<SomeInterface>?"), "?asso:x:SomeInterface")
> -    self.assertEquals(
> -        translate._MapKind("asso<SomeInterface&>?"), "?asso:r:x:SomeInterface")
> +    self.assertEquals(translate._MapKind("rca<SomeInterface>?"),
> +                      "?rca:x:SomeInterface")
> +
> +  def testSelfRecursiveUnions(self):
> +    """Verifies _UnionField() raises when a union is self-recursive."""
> +    tree = ast.Mojom(None, ast.ImportList(), [
> +        ast.Union("SomeUnion", None,
> +                  ast.UnionBody([ast.UnionField("a", None, None, "SomeUnion")]))
> +    ])
> +    with self.assertRaises(Exception):
> +      translate.OrderedModule(tree, "mojom_tree", [])
> +
> +    tree = ast.Mojom(None, ast.ImportList(), [
> +        ast.Union(
> +            "SomeUnion", None,
> +            ast.UnionBody([ast.UnionField("a", None, None, "SomeUnion?")]))
> +    ])
> +    with self.assertRaises(Exception):
> +      translate.OrderedModule(tree, "mojom_tree", [])
> +
> +  def testDuplicateAttributesException(self):
> +    tree = ast.Mojom(None, ast.ImportList(), [
> +        ast.Union(
> +            "FakeUnion",
> +            ast.AttributeList([
> +                ast.Attribute("key1", "value"),
> +                ast.Attribute("key1", "value")
> +            ]),
> +            ast.UnionBody([
> +                ast.UnionField("a", None, None, "int32"),
> +                ast.UnionField("b", None, None, "string")
> +            ]))
> +    ])
> +    with self.assertRaises(Exception):
> +      translate.OrderedModule(tree, "mojom_tree", [])
> +
> +  def testEnumWithReservedValues(self):
> +    """Verifies that assigning reserved values to enumerators fails."""
> +    # -128 is reserved for the empty representation in WTF::HashTraits.
> +    tree = ast.Mojom(None, ast.ImportList(), [
> +        ast.Enum(
> +            "MyEnum", None,
> +            ast.EnumValueList([
> +                ast.EnumValue('kReserved', None, '-128'),
> +            ]))
> +    ])
> +    with self.assertRaises(Exception) as context:
> +      translate.OrderedModule(tree, "mojom_tree", [])
> +    self.assertIn("reserved for WTF::HashTrait", str(context.exception))
> +
> +    # -127 is reserved for the deleted representation in WTF::HashTraits.
> +    tree = ast.Mojom(None, ast.ImportList(), [
> +        ast.Enum(
> +            "MyEnum", None,
> +            ast.EnumValueList([
> +                ast.EnumValue('kReserved', None, '-127'),
> +            ]))
> +    ])
> +    with self.assertRaises(Exception) as context:
> +      translate.OrderedModule(tree, "mojom_tree", [])
> +    self.assertIn("reserved for WTF::HashTrait", str(context.exception))
> +
> +    # Implicitly assigning a reserved value should also fail.
> +    tree = ast.Mojom(None, ast.ImportList(), [
> +        ast.Enum(
> +            "MyEnum", None,
> +            ast.EnumValueList([
> +                ast.EnumValue('kNotReserved', None, '-129'),
> +                ast.EnumValue('kImplicitlyReserved', None, None),
> +            ]))
> +    ])
> +    with self.assertRaises(Exception) as context:
> +      translate.OrderedModule(tree, "mojom_tree", [])
> +    self.assertIn("reserved for WTF::HashTrait", str(context.exception))
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/ast.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/ast.py
> index 1f0db200549b..aae9cdb659bd 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/parse/ast.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/ast.py
> @@ -1,4 +1,4 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Node classes for the AST for a Mojo IDL file."""
> @@ -8,17 +8,14 @@
>  # and lineno). You may also define __repr__() to help with analyzing test
>  # failures, especially for more complex types.
>  
> -
> -import sys
> +import os.path
>  
>  
> -def _IsStrOrUnicode(x):
> -  if sys.version_info[0] < 3:
> -    return isinstance(x, (unicode, str))
> -  return isinstance(x, str)
> +# Instance of 'NodeListBase' has no '_list_item_type' member (no-member)
> +# pylint: disable=no-member
>  
>  
> -class NodeBase(object):
> +class NodeBase:
>    """Base class for nodes in the AST."""
>  
>    def __init__(self, filename=None, lineno=None):
> @@ -43,7 +40,7 @@ class NodeListBase(NodeBase):
>    classes, in a tuple) of the members of the list.)"""
>  
>    def __init__(self, item_or_items=None, **kwargs):
> -    super(NodeListBase, self).__init__(**kwargs)
> +    super().__init__(**kwargs)
>      self.items = []
>      if item_or_items is None:
>        pass
> @@ -62,7 +59,7 @@ class NodeListBase(NodeBase):
>      return self.items.__iter__()
>  
>    def __eq__(self, other):
> -    return super(NodeListBase, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.items == other.items
>  
>    # Implement this so that on failure, we get slightly more sensible output.
> @@ -96,7 +93,7 @@ class Definition(NodeBase):
>    include parameter definitions.) This class is meant to be subclassed."""
>  
>    def __init__(self, mojom_name, **kwargs):
> -    assert _IsStrOrUnicode(mojom_name)
> +    assert isinstance(mojom_name, str)
>      NodeBase.__init__(self, **kwargs)
>      self.mojom_name = mojom_name
>  
> @@ -108,13 +105,13 @@ class Attribute(NodeBase):
>    """Represents an attribute."""
>  
>    def __init__(self, key, value, **kwargs):
> -    assert _IsStrOrUnicode(key)
> -    super(Attribute, self).__init__(**kwargs)
> +    assert isinstance(key, str)
> +    super().__init__(**kwargs)
>      self.key = key
>      self.value = value
>  
>    def __eq__(self, other):
> -    return super(Attribute, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.key == other.key and \
>             self.value == other.value
>  
> @@ -131,17 +128,17 @@ class Const(Definition):
>    def __init__(self, mojom_name, attribute_list, typename, value, **kwargs):
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
>      # The typename is currently passed through as a string.
> -    assert _IsStrOrUnicode(typename)
> +    assert isinstance(typename, str)
>      # The value is either a literal (currently passed through as a string) or a
>      # "wrapped identifier".
> -    assert _IsStrOrUnicode or isinstance(value, tuple)
> -    super(Const, self).__init__(mojom_name, **kwargs)
> +    assert isinstance(value, (tuple, str))
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.typename = typename
>      self.value = value
>  
>    def __eq__(self, other):
> -    return super(Const, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.typename == other.typename and \
>             self.value == other.value
> @@ -153,12 +150,12 @@ class Enum(Definition):
>    def __init__(self, mojom_name, attribute_list, enum_value_list, **kwargs):
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
>      assert enum_value_list is None or isinstance(enum_value_list, EnumValueList)
> -    super(Enum, self).__init__(mojom_name, **kwargs)
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.enum_value_list = enum_value_list
>  
>    def __eq__(self, other):
> -    return super(Enum, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.enum_value_list == other.enum_value_list
>  
> @@ -170,13 +167,13 @@ class EnumValue(Definition):
>      # The optional value is either an int (which is current a string) or a
>      # "wrapped identifier".
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
> -    assert value is None or _IsStrOrUnicode(value) or isinstance(value, tuple)
> -    super(EnumValue, self).__init__(mojom_name, **kwargs)
> +    assert value is None or isinstance(value, (tuple, str))
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.value = value
>  
>    def __eq__(self, other):
> -    return super(EnumValue, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.value == other.value
>  
> @@ -188,18 +185,47 @@ class EnumValueList(NodeListBase):
>    _list_item_type = EnumValue
>  
>  
> +class Feature(Definition):
> +  """Represents a runtime feature definition."""
> +  def __init__(self, mojom_name, attribute_list, body, **kwargs):
> +    assert attribute_list is None or isinstance(attribute_list, AttributeList)
> +    assert isinstance(body, FeatureBody) or body is None
> +    super().__init__(mojom_name, **kwargs)
> +    self.attribute_list = attribute_list
> +    self.body = body
> +
> +  def __eq__(self, other):
> +    return super().__eq__(other) and \
> +           self.attribute_list == other.attribute_list and \
> +           self.body == other.body
> +
> +  def __repr__(self):
> +    return "Feature(mojom_name = %s, attribute_list = %s, body = %s)" % (
> +        self.mojom_name, self.attribute_list, self.body)
> +
> +
> +# This needs to be declared after `FeatureConst` and `FeatureField`.
> +class FeatureBody(NodeListBase):
> +  """Represents the body of (i.e., list of definitions inside) a feature."""
> +
> +  # Features are compile time helpers so all fields are initializers/consts
> +  # for the underlying platform feature type.
> +  _list_item_type = (Const)
> +
> +
>  class Import(NodeBase):
>    """Represents an import statement."""
>  
>    def __init__(self, attribute_list, import_filename, **kwargs):
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
> -    assert _IsStrOrUnicode(import_filename)
> -    super(Import, self).__init__(**kwargs)
> +    assert isinstance(import_filename, str)
> +    super().__init__(**kwargs)
>      self.attribute_list = attribute_list
> -    self.import_filename = import_filename
> +    # TODO(crbug.com/953884): Use pathlib once we're migrated fully to Python 3.
> +    self.import_filename = os.path.normpath(import_filename).replace('\\', '/')
>  
>    def __eq__(self, other):
> -    return super(Import, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.import_filename == other.import_filename
>  
> @@ -216,12 +242,12 @@ class Interface(Definition):
>    def __init__(self, mojom_name, attribute_list, body, **kwargs):
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
>      assert isinstance(body, InterfaceBody)
> -    super(Interface, self).__init__(mojom_name, **kwargs)
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.body = body
>  
>    def __eq__(self, other):
> -    return super(Interface, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.body == other.body
>  
> @@ -236,14 +262,14 @@ class Method(Definition):
>      assert isinstance(parameter_list, ParameterList)
>      assert response_parameter_list is None or \
>             isinstance(response_parameter_list, ParameterList)
> -    super(Method, self).__init__(mojom_name, **kwargs)
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.ordinal = ordinal
>      self.parameter_list = parameter_list
>      self.response_parameter_list = response_parameter_list
>  
>    def __eq__(self, other):
> -    return super(Method, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.ordinal == other.ordinal and \
>             self.parameter_list == other.parameter_list and \
> @@ -264,12 +290,12 @@ class Module(NodeBase):
>      # |mojom_namespace| is either none or a "wrapped identifier".
>      assert mojom_namespace is None or isinstance(mojom_namespace, tuple)
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
> -    super(Module, self).__init__(**kwargs)
> +    super().__init__(**kwargs)
>      self.mojom_namespace = mojom_namespace
>      self.attribute_list = attribute_list
>  
>    def __eq__(self, other):
> -    return super(Module, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.mojom_namespace == other.mojom_namespace and \
>             self.attribute_list == other.attribute_list
>  
> @@ -281,13 +307,13 @@ class Mojom(NodeBase):
>      assert module is None or isinstance(module, Module)
>      assert isinstance(import_list, ImportList)
>      assert isinstance(definition_list, list)
> -    super(Mojom, self).__init__(**kwargs)
> +    super().__init__(**kwargs)
>      self.module = module
>      self.import_list = import_list
>      self.definition_list = definition_list
>  
>    def __eq__(self, other):
> -    return super(Mojom, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.module == other.module and \
>             self.import_list == other.import_list and \
>             self.definition_list == other.definition_list
> @@ -302,11 +328,11 @@ class Ordinal(NodeBase):
>  
>    def __init__(self, value, **kwargs):
>      assert isinstance(value, int)
> -    super(Ordinal, self).__init__(**kwargs)
> +    super().__init__(**kwargs)
>      self.value = value
>  
>    def __eq__(self, other):
> -    return super(Ordinal, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.value == other.value
>  
>  
> @@ -314,18 +340,18 @@ class Parameter(NodeBase):
>    """Represents a method request or response parameter."""
>  
>    def __init__(self, mojom_name, attribute_list, ordinal, typename, **kwargs):
> -    assert _IsStrOrUnicode(mojom_name)
> +    assert isinstance(mojom_name, str)
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
>      assert ordinal is None or isinstance(ordinal, Ordinal)
> -    assert _IsStrOrUnicode(typename)
> -    super(Parameter, self).__init__(**kwargs)
> +    assert isinstance(typename, str)
> +    super().__init__(**kwargs)
>      self.mojom_name = mojom_name
>      self.attribute_list = attribute_list
>      self.ordinal = ordinal
>      self.typename = typename
>  
>    def __eq__(self, other):
> -    return super(Parameter, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.mojom_name == other.mojom_name and \
>             self.attribute_list == other.attribute_list and \
>             self.ordinal == other.ordinal and \
> @@ -344,42 +370,51 @@ class Struct(Definition):
>    def __init__(self, mojom_name, attribute_list, body, **kwargs):
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
>      assert isinstance(body, StructBody) or body is None
> -    super(Struct, self).__init__(mojom_name, **kwargs)
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.body = body
>  
>    def __eq__(self, other):
> -    return super(Struct, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.body == other.body
>  
> +  def __repr__(self):
> +    return "Struct(mojom_name = %s, attribute_list = %s, body = %s)" % (
> +        self.mojom_name, self.attribute_list, self.body)
> +
>  
>  class StructField(Definition):
>    """Represents a struct field definition."""
>  
>    def __init__(self, mojom_name, attribute_list, ordinal, typename,
>                 default_value, **kwargs):
> -    assert _IsStrOrUnicode(mojom_name)
> +    assert isinstance(mojom_name, str)
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
>      assert ordinal is None or isinstance(ordinal, Ordinal)
> -    assert _IsStrOrUnicode(typename)
> +    assert isinstance(typename, str)
>      # The optional default value is currently either a value as a string or a
>      # "wrapped identifier".
> -    assert default_value is None or _IsStrOrUnicode(default_value) or \
> -        isinstance(default_value, tuple)
> -    super(StructField, self).__init__(mojom_name, **kwargs)
> +    assert default_value is None or isinstance(default_value, (str, tuple))
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.ordinal = ordinal
>      self.typename = typename
>      self.default_value = default_value
>  
>    def __eq__(self, other):
> -    return super(StructField, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.ordinal == other.ordinal and \
>             self.typename == other.typename and \
>             self.default_value == other.default_value
>  
> +  def __repr__(self):
> +    return ("StructField(mojom_name = %s, attribute_list = %s, ordinal = %s, "
> +            "typename = %s, default_value = %s") % (
> +                self.mojom_name, self.attribute_list, self.ordinal,
> +                self.typename, self.default_value)
> +
>  
>  # This needs to be declared after |StructField|.
>  class StructBody(NodeListBase):
> @@ -394,29 +429,29 @@ class Union(Definition):
>    def __init__(self, mojom_name, attribute_list, body, **kwargs):
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
>      assert isinstance(body, UnionBody)
> -    super(Union, self).__init__(mojom_name, **kwargs)
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.body = body
>  
>    def __eq__(self, other):
> -    return super(Union, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.body == other.body
>  
>  
>  class UnionField(Definition):
>    def __init__(self, mojom_name, attribute_list, ordinal, typename, **kwargs):
> -    assert _IsStrOrUnicode(mojom_name)
> +    assert isinstance(mojom_name, str)
>      assert attribute_list is None or isinstance(attribute_list, AttributeList)
>      assert ordinal is None or isinstance(ordinal, Ordinal)
> -    assert _IsStrOrUnicode(typename)
> -    super(UnionField, self).__init__(mojom_name, **kwargs)
> +    assert isinstance(typename, str)
> +    super().__init__(mojom_name, **kwargs)
>      self.attribute_list = attribute_list
>      self.ordinal = ordinal
>      self.typename = typename
>  
>    def __eq__(self, other):
> -    return super(UnionField, self).__eq__(other) and \
> +    return super().__eq__(other) and \
>             self.attribute_list == other.attribute_list and \
>             self.ordinal == other.ordinal and \
>             self.typename == other.typename
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/ast_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/ast_unittest.py
> index 62798631dbce..b289f7b11f66 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/parse/ast_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/ast_unittest.py
> @@ -1,32 +1,26 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import imp
> -import os.path
> -import sys
>  import unittest
>  
>  from mojom.parse import ast
>  
> -
>  class _TestNode(ast.NodeBase):
>    """Node type for tests."""
>  
>    def __init__(self, value, **kwargs):
> -    super(_TestNode, self).__init__(**kwargs)
> +    super().__init__(**kwargs)
>      self.value = value
>  
>    def __eq__(self, other):
> -    return super(_TestNode, self).__eq__(other) and self.value == other.value
> -
> +    return super().__eq__(other) and self.value == other.value
>  
>  class _TestNodeList(ast.NodeListBase):
>    """Node list type for tests."""
>  
>    _list_item_type = _TestNode
>  
> -
>  class ASTTest(unittest.TestCase):
>    """Tests various AST classes."""
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features.py
> index 3cb73c5d708c..9687edbfab1c 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features.py
> @@ -1,4 +1,4 @@
> -# Copyright 2018 The Chromium Authors. All rights reserved.
> +# Copyright 2018 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Helpers for processing conditionally enabled features in a mojom."""
> @@ -17,8 +17,10 @@ class EnableIfError(Error):
>  def _IsEnabled(definition, enabled_features):
>    """Returns true if a definition is enabled.
>  
> -  A definition is enabled if it has no EnableIf attribute, or if the value of
> -  the EnableIf attribute is in enabled_features.
> +  A definition is enabled if it has no EnableIf/EnableIfNot attribute.
> +  It is retained if it has an EnableIf attribute and the attribute is in
> +  enabled_features. It is retained if it has an EnableIfNot attribute and the
> +  attribute is not in enabled features.
>    """
>    if not hasattr(definition, "attribute_list"):
>      return True
> @@ -27,17 +29,19 @@ def _IsEnabled(definition, enabled_features):
>  
>    already_defined = False
>    for a in definition.attribute_list:
> -    if a.key == 'EnableIf':
> +    if a.key == 'EnableIf' or a.key == 'EnableIfNot':
>        if already_defined:
>          raise EnableIfError(
>              definition.filename,
> -            "EnableIf attribute may only be defined once per field.",
> +            "EnableIf/EnableIfNot attribute may only be set once per field.",
>              definition.lineno)
>        already_defined = True
>  
>    for attribute in definition.attribute_list:
>      if attribute.key == 'EnableIf' and attribute.value not in enabled_features:
>        return False
> +    if attribute.key == 'EnableIfNot' and attribute.value in enabled_features:
> +      return False
>    return True
>  
>  
> @@ -56,15 +60,12 @@ def _FilterDefinition(definition, enabled_features):
>    """Filters definitions with a body."""
>    if isinstance(definition, ast.Enum):
>      _FilterDisabledFromNodeList(definition.enum_value_list, enabled_features)
> -  elif isinstance(definition, ast.Interface):
> -    _FilterDisabledFromNodeList(definition.body, enabled_features)
>    elif isinstance(definition, ast.Method):
>      _FilterDisabledFromNodeList(definition.parameter_list, enabled_features)
>      _FilterDisabledFromNodeList(definition.response_parameter_list,
>                                  enabled_features)
> -  elif isinstance(definition, ast.Struct):
> -    _FilterDisabledFromNodeList(definition.body, enabled_features)
> -  elif isinstance(definition, ast.Union):
> +  elif isinstance(definition,
> +                  (ast.Interface, ast.Struct, ast.Union, ast.Feature)):
>      _FilterDisabledFromNodeList(definition.body, enabled_features)
>  
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features_unittest.py
> index aa609be73837..cca1764b1cd5 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features_unittest.py
> @@ -1,13 +1,12 @@
> -# Copyright 2018 The Chromium Authors. All rights reserved.
> +# Copyright 2018 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import imp
> +import importlib.util
>  import os
>  import sys
>  import unittest
>  
> -
>  def _GetDirAbove(dirname):
>    """Returns the directory "above" this file containing |dirname| (which must
>    also be "above" this file)."""
> @@ -18,9 +17,8 @@ def _GetDirAbove(dirname):
>      if tail == dirname:
>        return path
>  
> -
>  try:
> -  imp.find_module('mojom')
> +  importlib.util.find_spec("mojom")
>  except ImportError:
>    sys.path.append(os.path.join(_GetDirAbove('pylib'), 'pylib'))
>  import mojom.parse.ast as ast
> @@ -29,7 +27,6 @@ import mojom.parse.parser as parser
>  
>  ENABLED_FEATURES = frozenset({'red', 'green', 'blue'})
>  
> -
>  class ConditionalFeaturesTest(unittest.TestCase):
>    """Tests |mojom.parse.conditional_features|."""
>  
> @@ -55,6 +52,48 @@ class ConditionalFeaturesTest(unittest.TestCase):
>      """
>      self.parseAndAssertEqual(const_source, expected_source)
>  
> +  def testFilterIfNotConst(self):
> +    """Test that Consts are correctly filtered."""
> +    const_source = """
> +      [EnableIfNot=blue]
> +      const int kMyConst1 = 1;
> +      [EnableIfNot=orange]
> +      const double kMyConst2 = 2;
> +      [EnableIf=blue]
> +      const int kMyConst3 = 3;
> +      [EnableIfNot=blue]
> +      const int kMyConst4 = 4;
> +      [EnableIfNot=purple]
> +      const int kMyConst5 = 5;
> +    """
> +    expected_source = """
> +      [EnableIfNot=orange]
> +      const double kMyConst2 = 2;
> +      [EnableIf=blue]
> +      const int kMyConst3 = 3;
> +      [EnableIfNot=purple]
> +      const int kMyConst5 = 5;
> +    """
> +    self.parseAndAssertEqual(const_source, expected_source)
> +
> +  def testFilterIfNotMultipleConst(self):
> +    """Test that Consts are correctly filtered."""
> +    const_source = """
> +      [EnableIfNot=blue]
> +      const int kMyConst1 = 1;
> +      [EnableIfNot=orange]
> +      const double kMyConst2 = 2;
> +      [EnableIfNot=orange]
> +      const int kMyConst3 = 3;
> +    """
> +    expected_source = """
> +      [EnableIfNot=orange]
> +      const double kMyConst2 = 2;
> +      [EnableIfNot=orange]
> +      const int kMyConst3 = 3;
> +    """
> +    self.parseAndAssertEqual(const_source, expected_source)
> +
>    def testFilterEnum(self):
>      """Test that EnumValues are correctly filtered from an Enum."""
>      enum_source = """
> @@ -91,6 +130,24 @@ class ConditionalFeaturesTest(unittest.TestCase):
>      """
>      self.parseAndAssertEqual(import_source, expected_source)
>  
> +  def testFilterIfNotImport(self):
> +    """Test that imports are correctly filtered from a Mojom."""
> +    import_source = """
> +      [EnableIf=blue]
> +      import "foo.mojom";
> +      [EnableIfNot=purple]
> +      import "bar.mojom";
> +      [EnableIfNot=green]
> +      import "baz.mojom";
> +    """
> +    expected_source = """
> +      [EnableIf=blue]
> +      import "foo.mojom";
> +      [EnableIfNot=purple]
> +      import "bar.mojom";
> +    """
> +    self.parseAndAssertEqual(import_source, expected_source)
> +
>    def testFilterInterface(self):
>      """Test that definitions are correctly filtered from an Interface."""
>      interface_source = """
> @@ -175,6 +232,50 @@ class ConditionalFeaturesTest(unittest.TestCase):
>      """
>      self.parseAndAssertEqual(struct_source, expected_source)
>  
> +  def testFilterIfNotStruct(self):
> +    """Test that definitions are correctly filtered from a Struct."""
> +    struct_source = """
> +      struct MyStruct {
> +        [EnableIf=blue]
> +        enum MyEnum {
> +          VALUE1,
> +          [EnableIfNot=red]
> +          VALUE2,
> +        };
> +        [EnableIfNot=yellow]
> +        const double kMyConst = 1.23;
> +        [EnableIf=green]
> +        int32 a;
> +        double b;
> +        [EnableIfNot=purple]
> +        int32 c;
> +        [EnableIf=blue]
> +        double d;
> +        int32 e;
> +        [EnableIfNot=red]
> +        double f;
> +      };
> +    """
> +    expected_source = """
> +      struct MyStruct {
> +        [EnableIf=blue]
> +        enum MyEnum {
> +          VALUE1,
> +        };
> +        [EnableIfNot=yellow]
> +        const double kMyConst = 1.23;
> +        [EnableIf=green]
> +        int32 a;
> +        double b;
> +        [EnableIfNot=purple]
> +        int32 c;
> +        [EnableIf=blue]
> +        double d;
> +        int32 e;
> +      };
> +    """
> +    self.parseAndAssertEqual(struct_source, expected_source)
> +
>    def testFilterUnion(self):
>      """Test that UnionFields are correctly filtered from a Union."""
>      union_source = """
> @@ -216,6 +317,25 @@ class ConditionalFeaturesTest(unittest.TestCase):
>      """
>      self.parseAndAssertEqual(mojom_source, expected_source)
>  
> +  def testFeaturesWithEnableIf(self):
> +    mojom_source = """
> +      feature Foo {
> +        const string name = "FooFeature";
> +        [EnableIf=red]
> +        const bool default_state = false;
> +        [EnableIf=yellow]
> +        const bool default_state = true;
> +      };
> +    """
> +    expected_source = """
> +      feature Foo {
> +        const string name = "FooFeature";
> +        [EnableIf=red]
> +        const bool default_state = false;
> +      };
> +    """
> +    self.parseAndAssertEqual(mojom_source, expected_source)
> +
>    def testMultipleEnableIfs(self):
>      source = """
>        enum Foo {
> @@ -228,6 +348,29 @@ class ConditionalFeaturesTest(unittest.TestCase):
>                        conditional_features.RemoveDisabledDefinitions,
>                        definition, ENABLED_FEATURES)
>  
> +  def testMultipleEnableIfs(self):
> +    source = """
> +      enum Foo {
> +        [EnableIf=red,EnableIfNot=yellow]
> +        kBarValue = 5,
> +      };
> +    """
> +    definition = parser.Parse(source, "my_file.mojom")
> +    self.assertRaises(conditional_features.EnableIfError,
> +                      conditional_features.RemoveDisabledDefinitions,
> +                      definition, ENABLED_FEATURES)
> +
> +  def testMultipleEnableIfs(self):
> +    source = """
> +      enum Foo {
> +        [EnableIfNot=red,EnableIfNot=yellow]
> +        kBarValue = 5,
> +      };
> +    """
> +    definition = parser.Parse(source, "my_file.mojom")
> +    self.assertRaises(conditional_features.EnableIfError,
> +                      conditional_features.RemoveDisabledDefinitions,
> +                      definition, ENABLED_FEATURES)
>  
>  if __name__ == '__main__':
>    unittest.main()
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/lexer.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/lexer.py
> index 3e084bbf22b7..00136a8bf94a 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/parse/lexer.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/lexer.py
> @@ -1,8 +1,7 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import imp
>  import os.path
>  import sys
>  
> @@ -22,7 +21,7 @@ class LexError(Error):
>  
>  # We have methods which look like they could be functions:
>  # pylint: disable=R0201
> -class Lexer(object):
> +class Lexer:
>    def __init__(self, filename):
>      self.filename = filename
>  
> @@ -56,6 +55,7 @@ class Lexer(object):
>        'PENDING_RECEIVER',
>        'PENDING_ASSOCIATED_REMOTE',
>        'PENDING_ASSOCIATED_RECEIVER',
> +      'FEATURE',
>    )
>  
>    keyword_map = {}
> @@ -81,7 +81,6 @@ class Lexer(object):
>        # Operators
>        'MINUS',
>        'PLUS',
> -      'AMP',
>        'QSTN',
>  
>        # Assignment
> @@ -168,7 +167,6 @@ class Lexer(object):
>    # Operators
>    t_MINUS = r'-'
>    t_PLUS = r'\+'
> -  t_AMP = r'&'
>    t_QSTN = r'\?'
>  
>    # =
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/lexer_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/lexer_unittest.py
> index eadc6587cf94..bc9f8354316f 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/parse/lexer_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/lexer_unittest.py
> @@ -1,13 +1,12 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import imp
> +import importlib.util
>  import os.path
>  import sys
>  import unittest
>  
> -
>  def _GetDirAbove(dirname):
>    """Returns the directory "above" this file containing |dirname| (which must
>    also be "above" this file)."""
> @@ -18,17 +17,15 @@ def _GetDirAbove(dirname):
>      if tail == dirname:
>        return path
>  
> -
>  sys.path.insert(1, os.path.join(_GetDirAbove("mojo"), "third_party"))
>  from ply import lex
>  
>  try:
> -  imp.find_module("mojom")
> +  importlib.util.find_spec("mojom")
>  except ImportError:
>    sys.path.append(os.path.join(_GetDirAbove("pylib"), "pylib"))
>  import mojom.parse.lexer
>  
> -
>  # This (monkey-patching LexToken to make comparison value-based) is evil, but
>  # we'll do it anyway. (I'm pretty sure ply's lexer never cares about comparing
>  # for object identity.)
> @@ -146,7 +143,6 @@ class LexerTest(unittest.TestCase):
>          self._SingleTokenForInput("+"), _MakeLexToken("PLUS", "+"))
>      self.assertEquals(
>          self._SingleTokenForInput("-"), _MakeLexToken("MINUS", "-"))
> -    self.assertEquals(self._SingleTokenForInput("&"), _MakeLexToken("AMP", "&"))
>      self.assertEquals(
>          self._SingleTokenForInput("?"), _MakeLexToken("QSTN", "?"))
>      self.assertEquals(
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/parser.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/parser.py
> index b3b803d6f334..1dffd98b92a6 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/parse/parser.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/parser.py
> @@ -1,8 +1,11 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Generates a syntax tree from a Mojo IDL file."""
>  
> +# Breaking parser stanzas is unhelpful so allow longer lines.
> +# pylint: disable=line-too-long
> +
>  import os.path
>  import sys
>  
> @@ -33,7 +36,7 @@ class ParseError(Error):
>  
>  # We have methods which look like they could be functions:
>  # pylint: disable=R0201
> -class Parser(object):
> +class Parser:
>    def __init__(self, lexer, source, filename):
>      self.tokens = lexer.tokens
>      self.source = source
> @@ -111,7 +114,8 @@ class Parser(object):
>                    | union
>                    | interface
>                    | enum
> -                  | const"""
> +                  | const
> +                  | feature"""
>      p[0] = p[1]
>  
>    def p_attribute_section_1(self, p):
> @@ -140,12 +144,19 @@ class Parser(object):
>      p[0].Append(p[3])
>  
>    def p_attribute_1(self, p):
> -    """attribute : NAME EQUALS evaled_literal
> -                 | NAME EQUALS NAME"""
> -    p[0] = ast.Attribute(p[1], p[3], filename=self.filename, lineno=p.lineno(1))
> +    """attribute : name_wrapped EQUALS identifier_wrapped"""
> +    p[0] = ast.Attribute(p[1],
> +                         p[3][1],
> +                         filename=self.filename,
> +                         lineno=p.lineno(1))
>  
>    def p_attribute_2(self, p):
> -    """attribute : NAME"""
> +    """attribute : name_wrapped EQUALS evaled_literal
> +                 | name_wrapped EQUALS name_wrapped"""
> +    p[0] = ast.Attribute(p[1], p[3], filename=self.filename, lineno=p.lineno(1))
> +
> +  def p_attribute_3(self, p):
> +    """attribute : name_wrapped"""
>      p[0] = ast.Attribute(p[1], True, filename=self.filename, lineno=p.lineno(1))
>  
>    def p_evaled_literal(self, p):
> @@ -161,11 +172,11 @@ class Parser(object):
>        p[0] = eval(p[1])
>  
>    def p_struct_1(self, p):
> -    """struct : attribute_section STRUCT NAME LBRACE struct_body RBRACE SEMI"""
> +    """struct : attribute_section STRUCT name_wrapped LBRACE struct_body RBRACE SEMI"""
>      p[0] = ast.Struct(p[3], p[1], p[5])
>  
>    def p_struct_2(self, p):
> -    """struct : attribute_section STRUCT NAME SEMI"""
> +    """struct : attribute_section STRUCT name_wrapped SEMI"""
>      p[0] = ast.Struct(p[3], p[1], None)
>  
>    def p_struct_body_1(self, p):
> @@ -180,11 +191,24 @@ class Parser(object):
>      p[0].Append(p[2])
>  
>    def p_struct_field(self, p):
> -    """struct_field : attribute_section typename NAME ordinal default SEMI"""
> +    """struct_field : attribute_section typename name_wrapped ordinal default SEMI"""
>      p[0] = ast.StructField(p[3], p[1], p[4], p[2], p[5])
>  
> +  def p_feature(self, p):
> +    """feature : attribute_section FEATURE NAME LBRACE feature_body RBRACE SEMI"""
> +    p[0] = ast.Feature(p[3], p[1], p[5])
> +
> +  def p_feature_body_1(self, p):
> +    """feature_body : """
> +    p[0] = ast.FeatureBody()
> +
> +  def p_feature_body_2(self, p):
> +    """feature_body : feature_body const"""
> +    p[0] = p[1]
> +    p[0].Append(p[2])
> +
>    def p_union(self, p):
> -    """union : attribute_section UNION NAME LBRACE union_body RBRACE SEMI"""
> +    """union : attribute_section UNION name_wrapped LBRACE union_body RBRACE SEMI"""
>      p[0] = ast.Union(p[3], p[1], p[5])
>  
>    def p_union_body_1(self, p):
> @@ -197,7 +221,7 @@ class Parser(object):
>      p[1].Append(p[2])
>  
>    def p_union_field(self, p):
> -    """union_field : attribute_section typename NAME ordinal SEMI"""
> +    """union_field : attribute_section typename name_wrapped ordinal SEMI"""
>      p[0] = ast.UnionField(p[3], p[1], p[4], p[2])
>  
>    def p_default_1(self, p):
> @@ -209,8 +233,7 @@ class Parser(object):
>      p[0] = p[2]
>  
>    def p_interface(self, p):
> -    """interface : attribute_section INTERFACE NAME LBRACE interface_body \
> -                       RBRACE SEMI"""
> +    """interface : attribute_section INTERFACE name_wrapped LBRACE interface_body RBRACE SEMI"""
>      p[0] = ast.Interface(p[3], p[1], p[5])
>  
>    def p_interface_body_1(self, p):
> @@ -233,8 +256,7 @@ class Parser(object):
>      p[0] = p[3]
>  
>    def p_method(self, p):
> -    """method : attribute_section NAME ordinal LPAREN parameter_list RPAREN \
> -                    response SEMI"""
> +    """method : attribute_section name_wrapped ordinal LPAREN parameter_list RPAREN response SEMI"""
>      p[0] = ast.Method(p[2], p[1], p[3], p[5], p[7])
>  
>    def p_parameter_list_1(self, p):
> @@ -255,7 +277,7 @@ class Parser(object):
>      p[0].Append(p[3])
>  
>    def p_parameter(self, p):
> -    """parameter : attribute_section typename NAME ordinal"""
> +    """parameter : attribute_section typename name_wrapped ordinal"""
>      p[0] = ast.Parameter(
>          p[3], p[1], p[4], p[2], filename=self.filename, lineno=p.lineno(3))
>  
> @@ -271,8 +293,7 @@ class Parser(object):
>      """nonnullable_typename : basictypename
>                              | array
>                              | fixed_array
> -                            | associative_array
> -                            | interfacerequest"""
> +                            | associative_array"""
>      p[0] = p[1]
>  
>    def p_basictypename(self, p):
> @@ -297,18 +318,16 @@ class Parser(object):
>      p[0] = "rcv<%s>" % p[3]
>  
>    def p_associatedremotetype(self, p):
> -    """associatedremotetype : PENDING_ASSOCIATED_REMOTE LANGLE identifier \
> -                                  RANGLE"""
> +    """associatedremotetype : PENDING_ASSOCIATED_REMOTE LANGLE identifier RANGLE"""
>      p[0] = "rma<%s>" % p[3]
>  
>    def p_associatedreceivertype(self, p):
> -    """associatedreceivertype : PENDING_ASSOCIATED_RECEIVER LANGLE identifier \
> -                                    RANGLE"""
> +    """associatedreceivertype : PENDING_ASSOCIATED_RECEIVER LANGLE identifier RANGLE"""
>      p[0] = "rca<%s>" % p[3]
>  
>    def p_handletype(self, p):
>      """handletype : HANDLE
> -                  | HANDLE LANGLE NAME RANGLE"""
> +                  | HANDLE LANGLE name_wrapped RANGLE"""
>      if len(p) == 2:
>        p[0] = p[1]
>      else:
> @@ -342,14 +361,6 @@ class Parser(object):
>      """associative_array : MAP LANGLE identifier COMMA typename RANGLE"""
>      p[0] = p[5] + "{" + p[3] + "}"
>  
> -  def p_interfacerequest(self, p):
> -    """interfacerequest : identifier AMP
> -                        | ASSOCIATED identifier AMP"""
> -    if len(p) == 3:
> -      p[0] = p[1] + "&"
> -    else:
> -      p[0] = "asso<" + p[2] + "&>"
> -
>    def p_ordinal_1(self, p):
>      """ordinal : """
>      p[0] = None
> @@ -366,15 +377,14 @@ class Parser(object):
>      p[0] = ast.Ordinal(value, filename=self.filename, lineno=p.lineno(1))
>  
>    def p_enum_1(self, p):
> -    """enum : attribute_section ENUM NAME LBRACE enum_value_list \
> -                  RBRACE SEMI
> -            | attribute_section ENUM NAME LBRACE nonempty_enum_value_list \
> -                  COMMA RBRACE SEMI"""
> +    """enum : attribute_section ENUM name_wrapped LBRACE enum_value_list RBRACE SEMI
> +            | attribute_section ENUM name_wrapped LBRACE \
> +                    nonempty_enum_value_list COMMA RBRACE SEMI"""
>      p[0] = ast.Enum(
>          p[3], p[1], p[5], filename=self.filename, lineno=p.lineno(2))
>  
>    def p_enum_2(self, p):
> -    """enum : attribute_section ENUM NAME SEMI"""
> +    """enum : attribute_section ENUM name_wrapped SEMI"""
>      p[0] = ast.Enum(
>          p[3], p[1], None, filename=self.filename, lineno=p.lineno(2))
>  
> @@ -396,9 +406,9 @@ class Parser(object):
>      p[0].Append(p[3])
>  
>    def p_enum_value(self, p):
> -    """enum_value : attribute_section NAME
> -                  | attribute_section NAME EQUALS int
> -                  | attribute_section NAME EQUALS identifier_wrapped"""
> +    """enum_value : attribute_section name_wrapped
> +                  | attribute_section name_wrapped EQUALS int
> +                  | attribute_section name_wrapped EQUALS identifier_wrapped"""
>      p[0] = ast.EnumValue(
>          p[2],
>          p[1],
> @@ -407,7 +417,7 @@ class Parser(object):
>          lineno=p.lineno(2))
>  
>    def p_const(self, p):
> -    """const : attribute_section CONST typename NAME EQUALS constant SEMI"""
> +    """const : attribute_section CONST typename name_wrapped EQUALS constant SEMI"""
>      p[0] = ast.Const(p[4], p[1], p[3], p[6])
>  
>    def p_constant(self, p):
> @@ -422,10 +432,16 @@ class Parser(object):
>    # TODO(vtl): Make this produce a "wrapped" identifier (probably as an
>    # |ast.Identifier|, to be added) and get rid of identifier_wrapped.
>    def p_identifier(self, p):
> -    """identifier : NAME
> -                  | NAME DOT identifier"""
> +    """identifier : name_wrapped
> +                  | name_wrapped DOT identifier"""
>      p[0] = ''.join(p[1:])
>  
> +  # Allow 'feature' to be a name literal not just a keyword.
> +  def p_name_wrapped(self, p):
> +    """name_wrapped : NAME
> +                    | FEATURE"""
> +    p[0] = p[1]
> +
>    def p_literal(self, p):
>      """literal : int
>                 | float
> @@ -458,6 +474,12 @@ class Parser(object):
>        # TODO(vtl): Can we figure out what's missing?
>        raise ParseError(self.filename, "Unexpected end of file")
>  
> +    if e.value == 'feature':
> +      raise ParseError(self.filename,
> +                       "`feature` is reserved for a future mojom keyword",
> +                       lineno=e.lineno,
> +                       snippet=self._GetSnippet(e.lineno))
> +
>      raise ParseError(
>          self.filename,
>          "Unexpected %r:" % e.value,
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/parser_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/parser_unittest.py
> index 6d6b71532410..0a26307b1a32 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom/parse/parser_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/parser_unittest.py
> @@ -1,17 +1,13 @@
> -# Copyright 2014 The Chromium Authors. All rights reserved.
> +# Copyright 2014 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> -import imp
> -import os.path
> -import sys
>  import unittest
>  
>  from mojom.parse import ast
>  from mojom.parse import lexer
>  from mojom.parse import parser
>  
> -
>  class ParserTest(unittest.TestCase):
>    """Tests |parser.Parse()|."""
>  
> @@ -1086,7 +1082,7 @@ class ParserTest(unittest.TestCase):
>            handle<data_pipe_producer>? k;
>            handle<message_pipe>? l;
>            handle<shared_buffer>? m;
> -          some_interface&? n;
> +          pending_receiver<some_interface>? n;
>            handle<platform>? o;
>          };
>          """
> @@ -1110,7 +1106,7 @@ class ParserTest(unittest.TestCase):
>                  ast.StructField('l', None, None, 'handle<message_pipe>?', None),
>                  ast.StructField('m', None, None, 'handle<shared_buffer>?',
>                                  None),
> -                ast.StructField('n', None, None, 'some_interface&?', None),
> +                ast.StructField('n', None, None, 'rcv<some_interface>?', None),
>                  ast.StructField('o', None, None, 'handle<platform>?', None)
>              ]))
>      ])
> @@ -1138,16 +1134,6 @@ class ParserTest(unittest.TestCase):
>          r" *handle\?<data_pipe_consumer> a;$"):
>        parser.Parse(source2, "my_file.mojom")
>  
> -    source3 = """\
> -        struct MyStruct {
> -          some_interface?& a;
> -        };
> -        """
> -    with self.assertRaisesRegexp(
> -        parser.ParseError, r"^my_file\.mojom:2: Error: Unexpected '&':\n"
> -        r" *some_interface\?& a;$"):
> -      parser.Parse(source3, "my_file.mojom")
> -
>    def testSimpleUnion(self):
>      """Tests a simple .mojom source that just defines a union."""
>      source = """\
> @@ -1317,9 +1303,9 @@ class ParserTest(unittest.TestCase):
>      source1 = """\
>          struct MyStruct {
>            associated MyInterface a;
> -          associated MyInterface& b;
> +          pending_associated_receiver<MyInterface> b;
>            associated MyInterface? c;
> -          associated MyInterface&? d;
> +          pending_associated_receiver<MyInterface>? d;
>          };
>          """
>      expected1 = ast.Mojom(None, ast.ImportList(), [
> @@ -1327,16 +1313,16 @@ class ParserTest(unittest.TestCase):
>              'MyStruct', None,
>              ast.StructBody([
>                  ast.StructField('a', None, None, 'asso<MyInterface>', None),
> -                ast.StructField('b', None, None, 'asso<MyInterface&>', None),
> +                ast.StructField('b', None, None, 'rca<MyInterface>', None),
>                  ast.StructField('c', None, None, 'asso<MyInterface>?', None),
> -                ast.StructField('d', None, None, 'asso<MyInterface&>?', None)
> +                ast.StructField('d', None, None, 'rca<MyInterface>?', None)
>              ]))
>      ])
>      self.assertEquals(parser.Parse(source1, "my_file.mojom"), expected1)
>  
>      source2 = """\
>          interface MyInterface {
> -          MyMethod(associated A a) =>(associated B& b);
> +          MyMethod(associated A a) =>(pending_associated_receiver<B> b);
>          };"""
>      expected2 = ast.Mojom(None, ast.ImportList(), [
>          ast.Interface(
> @@ -1344,10 +1330,10 @@ class ParserTest(unittest.TestCase):
>              ast.InterfaceBody(
>                  ast.Method(
>                      'MyMethod', None, None,
> -                    ast.ParameterList(
> -                        ast.Parameter('a', None, None, 'asso<A>')),
> -                    ast.ParameterList(
> -                        ast.Parameter('b', None, None, 'asso<B&>')))))
> +                    ast.ParameterList(ast.Parameter('a', None, None,
> +                                                    'asso<A>')),
> +                    ast.ParameterList(ast.Parameter('b', None, None,
> +                                                    'rca<B>')))))
>      ])
>      self.assertEquals(parser.Parse(source2, "my_file.mojom"), expected2)
>  
> @@ -1385,6 +1371,5 @@ class ParserTest(unittest.TestCase):
>          r" *associated\? MyInterface& a;$"):
>        parser.Parse(source3, "my_file.mojom")
>  
> -
>  if __name__ == "__main__":
>    unittest.main()
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom_parser.py b/utils/ipc/mojo/public/tools/mojom/mojom_parser.py
> index eb90c825f9bc..9693090e44ea 100755
> --- a/utils/ipc/mojo/public/tools/mojom/mojom_parser.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom_parser.py
> @@ -1,5 +1,5 @@
> -#!/usr/bin/env python
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +#!/usr/bin/env python3
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  """Parses mojom IDL files.
> @@ -11,6 +11,7 @@ generate usable language bindings.
>  """
>  
>  import argparse
> +import builtins
>  import codecs
>  import errno
>  import json
> @@ -19,6 +20,7 @@ import multiprocessing
>  import os
>  import os.path
>  import sys
> +import traceback
>  from collections import defaultdict
>  
>  from mojom.generate import module
> @@ -28,16 +30,12 @@ from mojom.parse import conditional_features
>  
>  
>  # Disable this for easier debugging.
> -# In Python 2, subprocesses just hang when exceptions are thrown :(.
> -_ENABLE_MULTIPROCESSING = sys.version_info[0] > 2
> +_ENABLE_MULTIPROCESSING = True
>  
> -if sys.version_info < (3, 4):
> -  _MULTIPROCESSING_USES_FORK = sys.platform.startswith('linux')
> -else:
> -  # https://docs.python.org/3/library/multiprocessing.html#:~:text=bpo-33725
> -  if __name__ == '__main__' and sys.platform == 'darwin':
> -    multiprocessing.set_start_method('fork')
> -  _MULTIPROCESSING_USES_FORK = multiprocessing.get_start_method() == 'fork'
> +# https://docs.python.org/3/library/multiprocessing.html#:~:text=bpo-33725
> +if __name__ == '__main__' and sys.platform == 'darwin':
> +  multiprocessing.set_start_method('fork')
> +_MULTIPROCESSING_USES_FORK = multiprocessing.get_start_method() == 'fork'
>  
>  
>  def _ResolveRelativeImportPath(path, roots):
> @@ -63,7 +61,7 @@ def _ResolveRelativeImportPath(path, roots):
>    raise ValueError('"%s" does not exist in any of %s' % (path, roots))
>  
>  
> -def _RebaseAbsolutePath(path, roots):
> +def RebaseAbsolutePath(path, roots):
>    """Rewrites an absolute file path as relative to an absolute directory path in
>    roots.
>  
> @@ -139,7 +137,7 @@ def _EnsureInputLoaded(mojom_abspath, module_path, abs_paths, asts,
>      # Already done.
>      return
>  
> -  for dep_abspath, dep_path in dependencies[mojom_abspath]:
> +  for dep_abspath, dep_path in sorted(dependencies[mojom_abspath]):
>      if dep_abspath not in loaded_modules:
>        _EnsureInputLoaded(dep_abspath, dep_path, abs_paths, asts, dependencies,
>                           loaded_modules, module_metadata)
> @@ -159,11 +157,19 @@ def _CollectAllowedImportsFromBuildMetadata(build_metadata_filename):
>  
>    def collect(metadata_filename):
>      processed_deps.add(metadata_filename)
> +
> +    # Paths in the metadata file are relative to the metadata file's dir.
> +    metadata_dir = os.path.abspath(os.path.dirname(metadata_filename))
> +
> +    def to_abs(s):
> +      return os.path.normpath(os.path.join(metadata_dir, s))
> +
>      with open(metadata_filename) as f:
>        metadata = json.load(f)
>        allowed_imports.update(
> -          map(os.path.normcase, map(os.path.normpath, metadata['sources'])))
> +          [os.path.normcase(to_abs(s)) for s in metadata['sources']])
>        for dep_metadata in metadata['deps']:
> +        dep_metadata = to_abs(dep_metadata)
>          if dep_metadata not in processed_deps:
>            collect(dep_metadata)
>  
> @@ -172,8 +178,7 @@ def _CollectAllowedImportsFromBuildMetadata(build_metadata_filename):
>  
>  
>  # multiprocessing helper.
> -def _ParseAstHelper(args):
> -  mojom_abspath, enabled_features = args
> +def _ParseAstHelper(mojom_abspath, enabled_features):
>    with codecs.open(mojom_abspath, encoding='utf-8') as f:
>      ast = parser.Parse(f.read(), mojom_abspath)
>      conditional_features.RemoveDisabledDefinitions(ast, enabled_features)
> @@ -181,8 +186,7 @@ def _ParseAstHelper(args):
>  
>  
>  # multiprocessing helper.
> -def _SerializeHelper(args):
> -  mojom_abspath, mojom_path = args
> +def _SerializeHelper(mojom_abspath, mojom_path):
>    module_path = os.path.join(_SerializeHelper.output_root_path,
>                               _GetModuleFilename(mojom_path))
>    module_dir = os.path.dirname(module_path)
> @@ -199,12 +203,33 @@ def _SerializeHelper(args):
>      _SerializeHelper.loaded_modules[mojom_abspath].Dump(f)
>  
>  
> -def _Shard(target_func, args, processes=None):
> -  args = list(args)
> +class _ExceptionWrapper:
> +  def __init__(self):
> +    # Do not capture exception object to ensure pickling works.
> +    self.formatted_trace = traceback.format_exc()
> +
> +
> +class _FuncWrapper:
> +  """Marshals exceptions and spreads args."""
> +
> +  def __init__(self, func):
> +    self._func = func
> +
> +  def __call__(self, args):
> +    # multiprocessing does not gracefully handle excptions.
> +    # https://crbug.com/1219044
> +    try:
> +      return self._func(*args)
> +    except:  # pylint: disable=bare-except
> +      return _ExceptionWrapper()
> +
> +
> +def _Shard(target_func, arg_list, processes=None):
> +  arg_list = list(arg_list)
>    if processes is None:
>      processes = multiprocessing.cpu_count()
>    # Seems optimal to have each process perform at least 2 tasks.
> -  processes = min(processes, len(args) // 2)
> +  processes = min(processes, len(arg_list) // 2)
>  
>    if sys.platform == 'win32':
>      # TODO(crbug.com/1190269) - we can't use more than 56
> @@ -213,13 +238,17 @@ def _Shard(target_func, args, processes=None):
>  
>    # Don't spin up processes unless there is enough work to merit doing so.
>    if not _ENABLE_MULTIPROCESSING or processes < 2:
> -    for result in map(target_func, args):
> -      yield result
> +    for arg_tuple in arg_list:
> +      yield target_func(*arg_tuple)
>      return
>  
>    pool = multiprocessing.Pool(processes=processes)
>    try:
> -    for result in pool.imap_unordered(target_func, args):
> +    wrapped_func = _FuncWrapper(target_func)
> +    for result in pool.imap_unordered(wrapped_func, arg_list):
> +      if isinstance(result, _ExceptionWrapper):
> +        sys.stderr.write(result.formatted_trace)
> +        sys.exit(1)
>        yield result
>    finally:
>      pool.close()
> @@ -230,6 +259,7 @@ def _Shard(target_func, args, processes=None):
>  def _ParseMojoms(mojom_files,
>                   input_root_paths,
>                   output_root_path,
> +                 module_root_paths,
>                   enabled_features,
>                   module_metadata,
>                   allowed_imports=None):
> @@ -245,8 +275,10 @@ def _ParseMojoms(mojom_files,
>          are based on the mojom's relative path, rebased onto this path.
>          Additionally, the script expects this root to contain already-generated
>          modules for any transitive dependencies not listed in mojom_files.
> +    module_root_paths: A list of absolute filesystem paths which contain
> +        already-generated modules for any non-transitive dependencies.
>      enabled_features: A list of enabled feature names, controlling which AST
> -        nodes are filtered by [EnableIf] attributes.
> +        nodes are filtered by [EnableIf] or [EnableIfNot] attributes.
>      module_metadata: A list of 2-tuples representing metadata key-value pairs to
>          attach to each compiled module output.
>  
> @@ -262,7 +294,7 @@ def _ParseMojoms(mojom_files,
>    loaded_modules = {}
>    input_dependencies = defaultdict(set)
>    mojom_files_to_parse = dict((os.path.normcase(abs_path),
> -                               _RebaseAbsolutePath(abs_path, input_root_paths))
> +                               RebaseAbsolutePath(abs_path, input_root_paths))
>                                for abs_path in mojom_files)
>    abs_paths = dict(
>        (path, abs_path) for abs_path, path in mojom_files_to_parse.items())
> @@ -274,7 +306,7 @@ def _ParseMojoms(mojom_files,
>      loaded_mojom_asts[mojom_abspath] = ast
>  
>    logging.info('Processing dependencies')
> -  for mojom_abspath, ast in loaded_mojom_asts.items():
> +  for mojom_abspath, ast in sorted(loaded_mojom_asts.items()):
>      invalid_imports = []
>      for imp in ast.import_list:
>        import_abspath = _ResolveRelativeImportPath(imp.import_filename,
> @@ -295,8 +327,8 @@ def _ParseMojoms(mojom_files,
>          # be parsed and have a module file sitting in a corresponding output
>          # location.
>          module_path = _GetModuleFilename(imp.import_filename)
> -        module_abspath = _ResolveRelativeImportPath(module_path,
> -                                                    [output_root_path])
> +        module_abspath = _ResolveRelativeImportPath(
> +            module_path, module_root_paths + [output_root_path])
>          with open(module_abspath, 'rb') as module_file:
>            loaded_modules[import_abspath] = module.Module.Load(module_file)
>  
> @@ -370,6 +402,15 @@ already present in the provided output root.""")
>        'based on the relative input path, rebased onto this root. Note that '
>        'ROOT is also searched for existing modules of any transitive imports '
>        'which were not included in the set of inputs.')
> +  arg_parser.add_argument(
> +      '--module-root',
> +      default=[],
> +      action='append',
> +      metavar='ROOT',
> +      dest='module_root_paths',
> +      help='Adds ROOT to the set of root paths to search for existing modules '
> +      'of non-transitive imports. Provided root paths are always searched in '
> +      'order from longest absolute path to shortest.')
>    arg_parser.add_argument(
>        '--mojoms',
>        nargs='+',
> @@ -396,9 +437,9 @@ already present in the provided output root.""")
>        help='Enables a named feature when parsing the given mojoms. Features '
>        'are identified by arbitrary string values. Specifying this flag with a '
>        'given FEATURE name will cause the parser to process any syntax elements '
> -      'tagged with an [EnableIf=FEATURE] attribute. If this flag is not '
> -      'provided for a given FEATURE, such tagged elements are discarded by the '
> -      'parser and will not be present in the compiled output.')
> +      'tagged with an [EnableIf=FEATURE] or [EnableIfNot] attribute. If this '
> +      'flag is not provided for a given FEATURE, such tagged elements are '
> +      'discarded by the parser and will not be present in the compiled output.')
>    arg_parser.add_argument(
>        '--check-imports',
>        dest='build_metadata_filename',
> @@ -436,6 +477,7 @@ already present in the provided output root.""")
>    mojom_files = list(map(os.path.abspath, args.mojom_files))
>    input_roots = list(map(os.path.abspath, args.input_root_paths))
>    output_root = os.path.abspath(args.output_root_path)
> +  module_roots = list(map(os.path.abspath, args.module_root_paths))
>  
>    if args.build_metadata_filename:
>      allowed_imports = _CollectAllowedImportsFromBuildMetadata(
> @@ -445,13 +487,16 @@ already present in the provided output root.""")
>  
>    module_metadata = list(
>        map(lambda kvp: tuple(kvp.split('=')), args.module_metadata))
> -  _ParseMojoms(mojom_files, input_roots, output_root, args.enabled_features,
> -               module_metadata, allowed_imports)
> +  _ParseMojoms(mojom_files, input_roots, output_root, module_roots,
> +               args.enabled_features, module_metadata, allowed_imports)
>    logging.info('Finished')
> -  # Exit without running GC, which can save multiple seconds due the large
> -  # number of object created.
> -  os._exit(0)
>  
>  
>  if __name__ == '__main__':
>    Run(sys.argv[1:])
> +  # Exit without running GC, which can save multiple seconds due to the large
> +  # number of object created. But flush is necessary as os._exit doesn't do
> +  # that.
> +  sys.stdout.flush()
> +  sys.stderr.flush()
> +  os._exit(0)
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom_parser_test_case.py b/utils/ipc/mojo/public/tools/mojom/mojom_parser_test_case.py
> index e213fbfa760f..f0ee6966ac20 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom_parser_test_case.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom_parser_test_case.py
> @@ -1,4 +1,4 @@
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -20,7 +20,7 @@ class MojomParserTestCase(unittest.TestCase):
>    resolution, and module serialization and deserialization."""
>  
>    def __init__(self, method_name):
> -    super(MojomParserTestCase, self).__init__(method_name)
> +    super().__init__(method_name)
>      self._temp_dir = None
>  
>    def setUp(self):
> @@ -67,7 +67,7 @@ class MojomParserTestCase(unittest.TestCase):
>      self.ParseMojoms([filename])
>      m = self.LoadModule(filename)
>      definitions = {}
> -    for kinds in (m.enums, m.structs, m.unions, m.interfaces):
> +    for kinds in (m.enums, m.structs, m.unions, m.interfaces, m.features):
>        for kind in kinds:
>          definitions[kind.mojom_name] = kind
>      return definitions
> diff --git a/utils/ipc/mojo/public/tools/mojom/mojom_parser_unittest.py b/utils/ipc/mojo/public/tools/mojom/mojom_parser_unittest.py
> index a93f34bacb41..353a2b6e2980 100644
> --- a/utils/ipc/mojo/public/tools/mojom/mojom_parser_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/mojom_parser_unittest.py
> @@ -1,7 +1,9 @@
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> +import json
> +
>  from mojom_parser_test_case import MojomParserTestCase
>  
>  
> @@ -119,15 +121,22 @@ class MojomParserTest(MojomParserTestCase):
>      c = 'c.mojom'
>      c_metadata = 'out/c.build_metadata'
>      self.WriteFile(a_metadata,
> -                   '{"sources": ["%s"], "deps": []}\n' % self.GetPath(a))
> +                   json.dumps({
> +                       "sources": [self.GetPath(a)],
> +                       "deps": []
> +                   }))
>      self.WriteFile(
>          b_metadata,
> -        '{"sources": ["%s"], "deps": ["%s"]}\n' % (self.GetPath(b),
> -                                                   self.GetPath(a_metadata)))
> +        json.dumps({
> +            "sources": [self.GetPath(b)],
> +            "deps": [self.GetPath(a_metadata)]
> +        }))
>      self.WriteFile(
>          c_metadata,
> -        '{"sources": ["%s"], "deps": ["%s"]}\n' % (self.GetPath(c),
> -                                                   self.GetPath(b_metadata)))
> +        json.dumps({
> +            "sources": [self.GetPath(c)],
> +            "deps": [self.GetPath(b_metadata)]
> +        }))
>      self.WriteFile(a, """\
>          module a;
>          struct Bar {};""")
> @@ -154,9 +163,15 @@ class MojomParserTest(MojomParserTestCase):
>      b = 'b.mojom'
>      b_metadata = 'out/b.build_metadata'
>      self.WriteFile(a_metadata,
> -                   '{"sources": ["%s"], "deps": []}\n' % self.GetPath(a))
> +                   json.dumps({
> +                       "sources": [self.GetPath(a)],
> +                       "deps": []
> +                   }))
>      self.WriteFile(b_metadata,
> -                   '{"sources": ["%s"], "deps": []}\n' % self.GetPath(b))
> +                   json.dumps({
> +                       "sources": [self.GetPath(b)],
> +                       "deps": []
> +                   }))
>      self.WriteFile(a, """\
>          module a;
>          struct Bar {};""")
> diff --git a/utils/ipc/mojo/public/tools/mojom/stable_attribute_unittest.py b/utils/ipc/mojo/public/tools/mojom/stable_attribute_unittest.py
> index d45ec5862999..d10d69c68b13 100644
> --- a/utils/ipc/mojo/public/tools/mojom/stable_attribute_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/stable_attribute_unittest.py
> @@ -1,4 +1,4 @@
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> diff --git a/utils/ipc/mojo/public/tools/mojom/union_unittest.py b/utils/ipc/mojo/public/tools/mojom/union_unittest.py
> new file mode 100644
> index 000000000000..6b2525e5c5d0
> --- /dev/null
> +++ b/utils/ipc/mojo/public/tools/mojom/union_unittest.py
> @@ -0,0 +1,44 @@
> +# Copyright 2022 The Chromium Authors
> +# Use of this source code is governed by a BSD-style license that can be
> +# found in the LICENSE file.
> +
> +from mojom_parser_test_case import MojomParserTestCase
> +
> +
> +class UnionTest(MojomParserTestCase):
> +  """Tests union parsing behavior."""
> +
> +  def testExtensibleMustHaveDefault(self):
> +    """Verifies that extensible unions must have a default field."""
> +    mojom = 'foo.mojom'
> +    self.WriteFile(mojom, 'module foo; [Extensible] union U { bool x; };')
> +    with self.assertRaisesRegexp(Exception, 'must specify a \[Default\]'):
> +      self.ParseMojoms([mojom])
> +
> +  def testExtensibleSingleDefault(self):
> +    """Verifies that extensible unions must not have multiple default fields."""
> +    mojom = 'foo.mojom'
> +    self.WriteFile(
> +        mojom, """\
> +               module foo;
> +               [Extensible] union U {
> +                 [Default] bool x;
> +                 [Default] bool y;
> +               };
> +               """)
> +    with self.assertRaisesRegexp(Exception, 'Multiple \[Default\] fields'):
> +      self.ParseMojoms([mojom])
> +
> +  def testExtensibleDefaultTypeValid(self):
> +    """Verifies that an extensible union's default field must be nullable or
> +    integral type."""
> +    mojom = 'foo.mojom'
> +    self.WriteFile(
> +        mojom, """\
> +               module foo;
> +               [Extensible] union U {
> +                 [Default] handle<message_pipe> p;
> +               };
> +               """)
> +    with self.assertRaisesRegexp(Exception, 'must be nullable or integral'):
> +      self.ParseMojoms([mojom])
> diff --git a/utils/ipc/mojo/public/tools/mojom/version_compatibility_unittest.py b/utils/ipc/mojo/public/tools/mojom/version_compatibility_unittest.py
> index 65db4dc9cf59..45e45ec55e69 100644
> --- a/utils/ipc/mojo/public/tools/mojom/version_compatibility_unittest.py
> +++ b/utils/ipc/mojo/public/tools/mojom/version_compatibility_unittest.py
> @@ -1,4 +1,4 @@
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -23,9 +23,12 @@ class VersionCompatibilityTest(MojomParserTestCase):
>  
>      checker = module.BackwardCompatibilityChecker()
>      compatibility_map = {}
> -    for name in old.keys():
> -      compatibility_map[name] = checker.IsBackwardCompatible(
> -          new[name], old[name])
> +    for name in old:
> +      try:
> +        compatibility_map[name] = checker.IsBackwardCompatible(
> +            new[name], old[name])
> +      except Exception:
> +        compatibility_map[name] = False
>      return compatibility_map
>  
>    def assertBackwardCompatible(self, old_mojom, new_mojom):
> @@ -60,40 +63,48 @@ class VersionCompatibilityTest(MojomParserTestCase):
>      """Adding a value to an existing version is not allowed, even if the old
>      enum was marked [Extensible]. Note that it is irrelevant whether or not the
>      new enum is marked [Extensible]."""
> -    self.assertNotBackwardCompatible('[Extensible] enum E { kFoo, kBar };',
> -                                     'enum E { kFoo, kBar, kBaz };')
>      self.assertNotBackwardCompatible(
> -        '[Extensible] enum E { kFoo, kBar };',
> -        '[Extensible] enum E { kFoo, kBar, kBaz };')
> +        '[Extensible] enum E { [Default] kFoo, kBar };',
> +        'enum E { kFoo, kBar, kBaz };')
>      self.assertNotBackwardCompatible(
> -        '[Extensible] enum E { kFoo, [MinVersion=1] kBar };',
> +        '[Extensible] enum E { [Default] kFoo, kBar };',
> +        '[Extensible] enum E { [Default] kFoo, kBar, kBaz };')
> +    self.assertNotBackwardCompatible(
> +        '[Extensible] enum E { [Default] kFoo, [MinVersion=1] kBar };',
>          'enum E { kFoo, [MinVersion=1] kBar, [MinVersion=1] kBaz };')
>  
>    def testEnumValueRemoval(self):
>      """Removal of an enum value is never valid even for [Extensible] enums."""
>      self.assertNotBackwardCompatible('enum E { kFoo, kBar };',
>                                       'enum E { kFoo };')
> -    self.assertNotBackwardCompatible('[Extensible] enum E { kFoo, kBar };',
> -                                     '[Extensible] enum E { kFoo };')
>      self.assertNotBackwardCompatible(
> -        '[Extensible] enum E { kA, [MinVersion=1] kB };',
> -        '[Extensible] enum E { kA, };')
> +        '[Extensible] enum E { [Default] kFoo, kBar };',
> +        '[Extensible] enum E { [Default] kFoo };')
>      self.assertNotBackwardCompatible(
> -        '[Extensible] enum E { kA, [MinVersion=1] kB, [MinVersion=1] kZ };',
> -        '[Extensible] enum E { kA, [MinVersion=1] kB };')
> +        '[Extensible] enum E { [Default] kA, [MinVersion=1] kB };',
> +        '[Extensible] enum E { [Default] kA, };')
> +    self.assertNotBackwardCompatible(
> +        """[Extensible] enum E {
> +          [Default] kA,
> +          [MinVersion=1] kB,
> +          [MinVersion=1] kZ };""",
> +        '[Extensible] enum E { [Default] kA, [MinVersion=1] kB };')
>  
>    def testNewExtensibleEnumValueWithMinVersion(self):
>      """Adding a new and properly [MinVersion]'d value to an [Extensible] enum
>      is a backward-compatible change. Note that it is irrelevant whether or not
>      the new enum is marked [Extensible]."""
> -    self.assertBackwardCompatible('[Extensible] enum E { kA, kB };',
> +    self.assertBackwardCompatible('[Extensible] enum E { [Default] kA, kB };',
>                                    'enum E { kA, kB, [MinVersion=1] kC };')
>      self.assertBackwardCompatible(
> -        '[Extensible] enum E { kA, kB };',
> -        '[Extensible] enum E { kA, kB, [MinVersion=1] kC };')
> +        '[Extensible] enum E { [Default] kA, kB };',
> +        '[Extensible] enum E { [Default] kA, kB, [MinVersion=1] kC };')
>      self.assertBackwardCompatible(
> -        '[Extensible] enum E { kA, [MinVersion=1] kB };',
> -        '[Extensible] enum E { kA, [MinVersion=1] kB, [MinVersion=2] kC };')
> +        '[Extensible] enum E { [Default] kA, [MinVersion=1] kB };',
> +        """[Extensible] enum E {
> +          [Default] kA,
> +          [MinVersion=1] kB,
> +          [MinVersion=2] kC };""")
>  
>    def testRenameEnumValue(self):
>      """Renaming an enum value does not affect backward-compatibility. Only
> @@ -161,14 +172,17 @@ class VersionCompatibilityTest(MojomParserTestCase):
>          'struct S {}; struct T { S s; };',
>          'struct S { [MinVersion=1] int32 x; }; struct T { S s; };')
>      self.assertBackwardCompatible(
> -        '[Extensible] enum E { kA }; struct S { E e; };',
> -        '[Extensible] enum E { kA, [MinVersion=1] kB }; struct S { E e; };')
> +        '[Extensible] enum E { [Default] kA }; struct S { E e; };',
> +        """[Extensible] enum E {
> +          [Default] kA,
> +          [MinVersion=1] kB };
> +          struct S { E e; };""")
>      self.assertNotBackwardCompatible(
>          'struct S {}; struct T { S s; };',
>          'struct S { int32 x; }; struct T { S s; };')
>      self.assertNotBackwardCompatible(
> -        '[Extensible] enum E { kA }; struct S { E e; };',
> -        '[Extensible] enum E { kA, kB }; struct S { E e; };')
> +        '[Extensible] enum E { [Default] kA }; struct S { E e; };',
> +        '[Extensible] enum E { [Default] kA, kB }; struct S { E e; };')
>  
>    def testNewStructFieldWithInvalidMinVersion(self):
>      """Adding a new field using an existing MinVersion breaks backward-
> @@ -305,14 +319,17 @@ class VersionCompatibilityTest(MojomParserTestCase):
>          'struct S {}; union U { S s; };',
>          'struct S { [MinVersion=1] int32 x; }; union U { S s; };')
>      self.assertBackwardCompatible(
> -        '[Extensible] enum E { kA }; union U { E e; };',
> -        '[Extensible] enum E { kA, [MinVersion=1] kB }; union U { E e; };')
> +        '[Extensible] enum E { [Default] kA }; union U { E e; };',
> +        """[Extensible] enum E {
> +          [Default] kA,
> +          [MinVersion=1] kB };
> +          union U { E e; };""")
>      self.assertNotBackwardCompatible(
>          'struct S {}; union U { S s; };',
>          'struct S { int32 x; }; union U { S s; };')
>      self.assertNotBackwardCompatible(
> -        '[Extensible] enum E { kA }; union U { E e; };',
> -        '[Extensible] enum E { kA, kB }; union U { E e; };')
> +        '[Extensible] enum E { [Default] kA }; union U { E e; };',
> +        '[Extensible] enum E { [Default] kA, kB }; union U { E e; };')
>  
>    def testNewUnionFieldWithInvalidMinVersion(self):
>      """Adding a new field using an existing MinVersion breaks backward-
> diff --git a/utils/ipc/mojo/public/tools/run_all_python_unittests.py b/utils/ipc/mojo/public/tools/run_all_python_unittests.py
> index b20109583071..98bce18cbb6d 100755
> --- a/utils/ipc/mojo/public/tools/run_all_python_unittests.py
> +++ b/utils/ipc/mojo/public/tools/run_all_python_unittests.py
> @@ -1,5 +1,5 @@
> -#!/usr/bin/env python
> -# Copyright 2020 The Chromium Authors. All rights reserved.
> +#!/usr/bin/env python3
> +# Copyright 2020 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.
>  
> @@ -8,11 +8,13 @@ import sys
>  
>  _TOOLS_DIR = os.path.dirname(__file__)
>  _MOJOM_DIR = os.path.join(_TOOLS_DIR, 'mojom')
> +_BINDINGS_DIR = os.path.join(_TOOLS_DIR, 'bindings')
>  _SRC_DIR = os.path.join(_TOOLS_DIR, os.path.pardir, os.path.pardir,
>                          os.path.pardir)
>  
>  # Ensure that the mojom library is discoverable.
>  sys.path.append(_MOJOM_DIR)
> +sys.path.append(_BINDINGS_DIR)
>  
>  # Help Python find typ in //third_party/catapult/third_party/typ/
>  sys.path.append(
> @@ -21,7 +23,7 @@ import typ
>  
>  
>  def Main():
> -  return typ.main(top_level_dir=_MOJOM_DIR)
> +  return typ.main(top_level_dirs=[_MOJOM_DIR, _BINDINGS_DIR])
>  
>  
>  if __name__ == '__main__':
> diff --git a/utils/ipc/tools/README b/utils/ipc/tools/README
> index d5c24fc3b5cb..961cabd222e3 100644
> --- a/utils/ipc/tools/README
> +++ b/utils/ipc/tools/README
> @@ -1,4 +1,4 @@
>  # SPDX-License-Identifier: CC0-1.0
>  
> -Files in this directory are imported from 9c138d992bfc of Chromium. Do not
> +Files in this directory are imported from 9be4263648d7 of Chromium. Do not
>  modify them manually.
> diff --git a/utils/ipc/tools/diagnosis/crbug_1001171.py b/utils/ipc/tools/diagnosis/crbug_1001171.py
> index 478fb8c1a610..40900d10d38a 100644
> --- a/utils/ipc/tools/diagnosis/crbug_1001171.py
> +++ b/utils/ipc/tools/diagnosis/crbug_1001171.py
> @@ -1,4 +1,4 @@
> -# Copyright 2019 The Chromium Authors. All rights reserved.
> +# Copyright 2019 The Chromium Authors
>  # Use of this source code is governed by a BSD-style license that can be
>  # found in the LICENSE file.



More information about the libcamera-devel mailing list