compositor-worker: Share a thread and an isolate for compositor workers.

Source/core/workers/WorkerThread.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 103 matching lines @@
     void setWorkerInspectorController(WorkerInspectorController*);
 
 protected:
     WorkerThread(PassRefPtr<WorkerLoaderProxy>, WorkerReportingProxy&);
 
     // Factory method for creating a new worker context for the thread.
     virtual PassRefPtrWillBeRawPtr<WorkerGlobalScope> createWorkerGlobalScope(PassOwnPtr<WorkerThreadStartupData>) = 0;
 
     virtual void postInitialize() { }
 
+    // Both of these methods are called in the worker thread.
+    virtual void initializeBackingThread();
+    virtual void shutdownBackingThread();
+
     virtual v8::Isolate* initializeIsolate();
     virtual void willDestroyIsolate();
     virtual void destroyIsolate();
     virtual void terminateV8Execution();
 
     // This is protected virtual for testing.
     virtual bool doIdleGc(double deadlineSeconds);
 
 private:
     friend class WorkerMicrotaskRunner;
@@ skipping 30 matching lines @@
     // Used to signal thread shutdown.
     OwnPtr<WebWaitableEvent> m_shutdownEvent;
 
     // Used to signal thread termination.
     OwnPtr<WebWaitableEvent> m_terminationEvent;
 };
 
 } // namespace blink
 
 #endif // WorkerThread_h