IDL: Support default values for dictionary members of union types

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 71 matching lines @@
 
     restricted_float = (
         has_extended_attribute_value(dictionary, 'TypeChecking', 'Unrestricted') or
         has_extended_attribute_value(member, 'TypeChecking', 'Unrestricted'))
 
     def default_values():
         if not member.default_value:
             return None, None
         if member.default_value.is_null:
             return None, 'v8::Null(isolate)'
-        cpp_default_value = str(member.default_value)
+        cpp_default_value = unwrapped_idl_type.literal_cpp_value(
+            member.default_value)
         v8_default_value = unwrapped_idl_type.cpp_value_to_v8_value(
             cpp_value=cpp_default_value, isolate='isolate',
             creation_context='creationContext')
         return cpp_default_value, v8_default_value
 
     cpp_default_value, v8_default_value = default_values()
     cpp_name = v8_utilities.cpp_name(member)
 
     return {
         'cpp_default_value': cpp_default_value,
@@ skipping 76 matching lines @@
             return 'm_%s' % cpp_name
 
     def member_cpp_type():
         member_cpp_type = idl_type.cpp_type_args(used_in_cpp_sequence=True)
         if idl_type.impl_should_use_nullable_container:
             return v8_types.cpp_template_type('Nullable', member_cpp_type)
         return member_cpp_type
 
     cpp_default_value = None
     if member.default_value and not member.default_value.is_null:
-        cpp_default_value = str(member.default_value)
+        cpp_default_value = idl_type.literal_cpp_value(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_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),
     }