IDL: Use IdlNullableType wrapper to represent nullable 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 copy
 import operator
 from v8_globals import includes
 import v8_types
 import v8_utilities
 
 
 DICTIONARY_H_INCLUDES = frozenset([
     'bindings/core/v8/V8Binding.h',
     'platform/heap/Handle.h',
 ])
@@ skipping 25 matching lines @@
                                          key=operator.attrgetter('name'))],
         'v8_class': v8_utilities.v8_class_name(dictionary),
     }
 
 
 def member_context(member):
     idl_type = member.idl_type
     idl_type.add_includes_for_type()
 
     def idl_type_for_default_value():
-        copied_type = copy.copy(idl_type)
-        # IdlType for default values shouldn't be nullable. Otherwise,
-        # it will generate meaningless expression like
-        # 'String("default value").isNull() ? ...'.
-        copied_type.is_nullable = False
-        return copied_type
+        if idl_type.is_nullable:
+            return idl_type.inner_type
+        return idl_type
 
     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)
         v8_default_value = idl_type_for_default_value().cpp_value_to_v8_value(
             cpp_value=cpp_default_value, isolate='isolate',
             creation_context='creationContext')
@@ skipping 60 matching lines @@
         '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),
     }