Introduce WorkerBackingThread

third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.h

Index: third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.h
diff --git a/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.h b/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.h
index 56cdba902ff4f6e883423ed7c970d7c814bfd86e..f097c68dd69bc61319d60d5788eb66718116a6a8 100644
--- a/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.h
+++ b/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.h
@@ -20,26 +20,14 @@ public:
 
     WorkerObjectProxy& workerObjectProxy() const { return m_workerObjectProxy; }
 
-    // Returns the shared backing thread for all CompositorWorkers.
-    static WebThreadSupportingGC* sharedBackingThread();
-
-    static bool hasThreadForTest();
-    static bool hasIsolateForTest();
+    static void resetSharedBackingThreadForTest();
+    static void clearSharedBackingThread();
 
 protected:
     CompositorWorkerThread(PassRefPtr<WorkerLoaderProxy>, WorkerObjectProxy&, double timeOrigin);
 
     // WorkerThread:
     PassRefPtrWillBeRawPtr<WorkerGlobalScope> createWorkerGlobalScope(PassOwnPtr<WorkerThreadStartupData>) override;
-    WebThreadSupportingGC& backingThread() override;
-    void didStartWorkerThread() override { }
-    void willStopWorkerThread() override { }
-    void initializeBackingThread() override;
-    void shutdownBackingThread() override;
-    v8::Isolate* initializeIsolate() override;
-    void willDestroyIsolate() override;
-    void destroyIsolate() override;
-    void terminateV8Execution() override;
 
 private:
     WorkerObjectProxy& m_workerObjectProxy;