IDL: Improve CG for attributes with [CachedAttribute]

Source/bindings/scripts/v8_attributes.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 173 matching lines @@
         'ReflectOnly' in extended_attributes or
         context['is_keep_alive_for_gc'] or
         context['is_getter_raises_exception']):
         context['cpp_value_original'] = cpp_value
         cpp_value = 'cppValue'
         # EventHandler has special handling
         if base_idl_type != 'EventHandler':
             release = idl_type.release
 
     def v8_set_return_value_statement(for_main_world=False):
-        if context['is_keep_alive_for_gc']:
-            return 'v8SetReturnValue(info, wrapper)'
-        return idl_type.v8_set_return_value(cpp_value, extended_attributes=extended_attributes, script_wrappable='impl', release=release, for_main_world=for_main_world)
+        if context['is_keep_alive_for_gc'] or 'CachedAttribute' in extended_attributes:
+            return 'v8SetReturnValue(info, v8Value)'
+        return idl_type.v8_set_return_value(
+            cpp_value, extended_attributes=extended_attributes, script_wrappable='impl',
+            release=release, for_main_world=for_main_world)
 
     context.update({
         'cpp_value': cpp_value,
         'cpp_value_to_v8_value': idl_type.cpp_value_to_v8_value(
             cpp_value=cpp_value, creation_context='info.Holder()',
             extended_attributes=extended_attributes),
         'v8_set_return_value_for_main_world': v8_set_return_value_statement(for_main_world=True),
         'v8_set_return_value': v8_set_return_value_statement(),
     })
 
-
 def getter_expression(interface, attribute, context):
     arguments = []
     this_getter_base_name = getter_base_name(interface, attribute, arguments)
     getter_name = scoped_name(interface, attribute, this_getter_base_name)
 
     if 'ImplementedInPrivateScript' in attribute.extended_attributes:
         arguments.append('toLocalFrame(toFrameIfNotDetached(info.GetIsolate()->GetCurrentContext()))')
         arguments.append('impl')
         arguments.append('&result')
     arguments.extend(v8_utilities.call_with_arguments(
@@ skipping 293 matching lines @@
     lambda self: strip_suffix(self.base_type, 'Constructor'))
 
 
 def is_constructor_attribute(attribute):
     # FIXME: replace this with [ConstructorAttribute] extended attribute
     return attribute.idl_type.name.endswith('Constructor')
 
 
 def constructor_getter_context(interface, attribute, context):
     context['needs_constructor_getter_callback'] = context['measure_as'] or context['deprecate_as']