[bindings] Implement an ExperimentEnabled IDL extended attribute.

third_party/WebKit/Source/bindings/scripts/v8_methods.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 106 matching lines @@
 
     if 'LenientThis' in extended_attributes:
         raise Exception('[LenientThis] is not supported for operations.')
 
     argument_contexts = [
         argument_context(interface, method, argument, index, is_visible=is_visible)
         for index, argument in enumerate(arguments)]
 
     return {
         'activity_logging_world_list': v8_utilities.activity_logging_world_list(method),  # [ActivityLogging]
+        'api_experiment_name': v8_utilities.api_experiment_name(method),  # [APIExperimentEnabled]
         'arguments': argument_contexts,
         'argument_declarations_for_private_script':
             argument_declarations_for_private_script(interface, method),
         'conditional_string': v8_utilities.conditional_string(method),
         'cpp_type': (v8_types.cpp_template_type('Nullable', idl_type.cpp_type)
                      if idl_type.is_explicit_nullable else idl_type.cpp_type),
         'cpp_value': this_cpp_value,
         'cpp_type_initializer': idl_type.cpp_type_initializer,
         'custom_registration_extended_attributes':
             CUSTOM_REGISTRATION_EXTENDED_ATTRIBUTES.intersection(
@@ skipping 336 matching lines @@
     return method.idl_type and method.idl_type.name == 'Promise'
 
 IdlOperation.returns_promise = property(method_returns_promise)
 
 
 def argument_conversion_needs_exception_state(method, argument):
     idl_type = argument.idl_type
     return (idl_type.v8_conversion_needs_exception_state or
             argument.is_variadic or
             (method.returns_promise and idl_type.is_string_type))