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 4e96a6b62789db18c17a8b8045825f56f5904afb..94a17e8e1dc79d84380a0d13bea728f095b15cbf 100644
--- a/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.h
+++ b/third_party/WebKit/Source/modules/compositorworker/CompositorWorkerThread.h
@@ -13,33 +13,22 @@ namespace blink {
 class WorkerObjectProxy;
 
 // This class is overridden in unit-tests.
-class MODULES_EXPORT CompositorWorkerThread : public WorkerThread {
+class MODULES_EXPORT CompositorWorkerThread final : public WorkerThread {
 public:
     static PassOwnPtr<CompositorWorkerThread> create(PassRefPtr<WorkerLoaderProxy>, WorkerObjectProxy&, double timeOrigin);
     ~CompositorWorkerThread() override;
 
     WorkerObjectProxy& workerObjectProxy() const { return m_workerObjectProxy; }
+    WorkerBackingThread& workerBackingThread() override;
+    bool shouldAttachThreadDebugger() const override { return false; }
 
-    // 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:
     RawPtr<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;