Prepare for per thread heap on service worker thread.

third_party/WebKit/Source/web/ServiceWorkerGlobalScopeProxy.h

 /*
  * 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
@@ skipping 101 matching lines @@
     Document& document() const;
     ServiceWorkerGlobalScope* workerGlobalScope() const;
 
     // Non-null until the WebEmbeddedWorkerImpl explicitly detach()es
     // as part of its finalization.
     WebEmbeddedWorkerImpl* m_embeddedWorker;
     Member<Document> m_document;
 
     WebServiceWorkerContextClient* m_client;
 
-    Member<ServiceWorkerGlobalScope> m_workerGlobalScope;
+    CrossThreadPersistent<ServiceWorkerGlobalScope> m_workerGlobalScope;
 };
 
 } // namespace blink
 
 #endif // ServiceWorkerGlobalScopeProxy_h