IDL: Set dictionary default values in impl constructor

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 copy
 import operator
@@ skipping 103 matching lines @@
             return '!m_%s.isNull()' % member.name
         else:
             return 'm_%s' % member.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)
+
     header_includes.update(idl_type.impl_includes_for_type(interfaces_info))
     return {
+        'cpp_default_value': cpp_default_value,
         'getter_expression': getter_expression(),
         'has_method_expression': has_method_expression(),
         'has_method_name': has_method_name_for_dictionary_member(member),
         'is_traceable': (idl_type.is_garbage_collected or
                          idl_type.is_will_be_garbage_collected),
         'member_cpp_type': member_cpp_type(),
         'name': member.name,
         'rvalue_cpp_type': idl_type.cpp_type_args(used_as_rvalue_type=True),
         'setter_name': setter_name_for_dictionary_member(member),
     }