Have bindings layer assume and insist that all interface types are GCed.

third_party/WebKit/Source/bindings/scripts/v8_dictionary.py

 # Copyright 2014 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.
 
 """Generate template contexts of dictionaries for both v8 bindings and
 implementation classes that are used by blink's core/modules.
 """
 
 import operator
 from idl_types import IdlType
@@ skipping 107 matching lines @@
         'cpp_type': unwrapped_idl_type.cpp_type,
         'cpp_value_to_v8_value': unwrapped_idl_type.cpp_value_to_v8_value(
             cpp_value='impl.%s()' % cpp_name, isolate='isolate',
             creation_context='creationContext',
             extended_attributes=extended_attributes),
         'deprecate_as': v8_utilities.deprecate_as(member),
         'enum_type': idl_type.enum_type,
         'enum_values': unwrapped_idl_type.enum_values,
         'has_method_name': has_method_name_for_dictionary_member(member),
         'idl_type': idl_type.base_type,
-        'is_interface_type': idl_type.is_interface_type and not (idl_type.is_dictionary_type or is_deprecated_dictionary),
+        'is_interface_type': idl_type.is_interface_type and not is_deprecated_dictionary,
         'is_nullable': idl_type.is_nullable,
         'is_object': unwrapped_idl_type.name == 'Object' or is_deprecated_dictionary,
         'is_required': member.is_required,
         'name': member.name,
         'runtime_enabled_function': v8_utilities.runtime_enabled_function_name(member),  # [RuntimeEnabled]
         'setter_name': setter_name_for_dictionary_member(member),
         'null_setter_name': null_setter_name_for_dictionary_member(member),
         'v8_default_value': v8_default_value,
         'v8_value_to_local_cpp_value': unwrapped_idl_type.v8_value_to_local_cpp_value(
             extended_attributes, member.name + 'Value',
@@ skipping 73 matching lines @@
         'getter_expression': getter_expression(),
         'has_method_expression': has_method_expression(),
         'has_method_name': has_method_name_for_dictionary_member(member),
         'is_nullable': idl_type.is_nullable,
         'is_traceable': idl_type.is_traceable,
         'member_cpp_type': member_cpp_type(),
         'null_setter_name': null_setter_name_for_dictionary_member(member),
         'rvalue_cpp_type': idl_type.cpp_type_args(used_as_rvalue_type=True),
         'setter_name': setter_name_for_dictionary_member(member),
     }