IDL: object type support for IDL dictionary

Source/core/testing/InternalDictionary.idl

 // 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.
 
 enum InternalEnum { "foo", "bar", "baz" };
 
 [
     GarbageCollected
 ] dictionary InternalDictionary {
     long longMember;
     long longMemberWithDefault = 42;
     long? longOrNullMember;
     long? longOrNullMemberWithDefault = null;
     boolean booleanMember;
     double doubleMember;
     DOMString stringMember;
     DOMString stringMemberWithDefault = "defaultStringValue";
     sequence<DOMString> stringSequenceMember;
     sequence<DOMString>? stringSequenceOrNullMember;
     InternalEnum enumMember;
     InternalEnum enumMemberWithDefault = "foo";
     InternalEnum? enumOrNullMember;
     Element elementMember;
     Element? elementOrNullMember;
+    object objectMember;
+    object? objectOrNullMemberWithDefault = null;
 };