IDL: Add IdlTypeBase.is_traceable

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 v8_globals import includes
@@ skipping 123 matching lines @@
         cpp_default_value = str(member.default_value)
 
     header_includes.update(idl_type.impl_includes_for_type(interfaces_info))
     return {
         'cpp_default_value': cpp_default_value,
         'cpp_name': cpp_name,
         'getter_expression': getter_expression(),
         'has_method_expression': has_method_expression(),
         'has_method_name': has_method_name_for_dictionary_member(member),
         'is_object': is_object,
-        'is_traceable': (idl_type.is_garbage_collected or
-                         idl_type.is_will_be_garbage_collected),
+        'is_traceable': idl_type.is_traceable,
         'member_cpp_type': member_cpp_type(),
         'rvalue_cpp_type': idl_type.cpp_type_args(used_as_rvalue_type=True),
         'setter_name': setter_name_for_dictionary_member(member),
     }