Oilpan: Prepare to make ExecutionContext GarbageCollectedMixin.

Source/core/workers/WorkerMessagingProxy.h

 /*
  * Copyright (C) 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 68 matching lines @@
         virtual bool postTaskToWorkerGlobalScope(PassOwnPtr<ExecutionContextTask>) OVERRIDE;
 
         void workerThreadCreated(PassRefPtr<DedicatedWorkerThread>);
 
     protected:
         virtual ~WorkerMessagingProxy();
 
     private:
         static void workerObjectDestroyedInternal(ExecutionContext*, WorkerMessagingProxy*);
 
-        RefPtr<ExecutionContext> m_executionContext;
+        RefPtrWillBePersistent<ExecutionContext> m_executionContext;
         OwnPtr<WorkerObjectProxy> m_workerObjectProxy;
         Worker* m_workerObject;
         bool m_mayBeDestroyed;
         RefPtr<DedicatedWorkerThread> m_workerThread;
 
         unsigned m_unconfirmedMessageCount; // Unconfirmed messages from worker object to worker thread.
         bool m_workerThreadHadPendingActivity; // The latest confirmation from worker thread reported that it was still active.
 
         bool m_askedToTerminate;
 
         Vector<OwnPtr<ExecutionContextTask> > m_queuedEarlyTasks; // Tasks are queued here until there's a thread object created.
         WorkerGlobalScopeProxy::PageInspector* m_pageInspector;
 
         OwnPtrWillBePersistent<WorkerClients> m_workerClients;
     };
 
 } // namespace WebCore
 
 #endif // WorkerMessagingProxy_h