[WIP] bindings: Introduce PropertyBag

Source/modules/serviceworkers/RegistrationOptionList.h

 // 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.
 
 #ifndef RegistrationOptionList_h
 #define RegistrationOptionList_h
 
 #include "bindings/core/v8/Dictionary.h"
 
 namespace blink {
 
 struct RegistrationOptionList  {
     explicit RegistrationOptionList(const Dictionary& options)
         : scope("/")
     {
         // FIXME: Should be ScalarValueString. http://crbug.com/379009
-        DictionaryHelper::get(options, "scope", scope);
+        options.get("scope", scope);
     }
 
     String scope;
 };
 
 } // namespace blink
 
 #endif // RegistrationOptionList_h