compositor-worker: Introduce CompositorWorker.

Source/core/workers/DedicatedWorkerThread.h

Index: Source/core/workers/DedicatedWorkerThread.h
diff --git a/Source/core/workers/DedicatedWorkerThread.h b/Source/core/workers/DedicatedWorkerThread.h
index ac6fa4b2cae44089d32d3f16d0ddbe4c5e5f5240..8544e8384cde5fe1752b8117d08a11a096dc74d2 100644
--- a/Source/core/workers/DedicatedWorkerThread.h
+++ b/Source/core/workers/DedicatedWorkerThread.h
@@ -38,19 +38,18 @@ namespace blink {
 class WorkerObjectProxy;
 class WorkerThreadStartupData;
 
-class DedicatedWorkerThread final : public WorkerThread {
+class DedicatedWorkerThread : public WorkerThread {
 public:
     static PassRefPtr<DedicatedWorkerThread> create(PassRefPtr<WorkerLoaderProxy>, WorkerObjectProxy&, double timeOrigin, PassOwnPtrWillBeRawPtr<WorkerThreadStartupData>);
     WorkerObjectProxy& workerObjectProxy() const { return m_workerObjectProxy; }
     virtual ~DedicatedWorkerThread();
 
 protected:
+    DedicatedWorkerThread(PassRefPtr<WorkerLoaderProxy>, WorkerObjectProxy&, double timeOrigin, PassOwnPtrWillBeRawPtr<WorkerThreadStartupData>);
     virtual PassRefPtrWillBeRawPtr<WorkerGlobalScope> createWorkerGlobalScope(PassOwnPtrWillBeRawPtr<WorkerThreadStartupData>) override;
     virtual void postInitialize() override;
 
 private:
-    DedicatedWorkerThread(PassRefPtr<WorkerLoaderProxy>, WorkerObjectProxy&, double timeOrigin, PassOwnPtrWillBeRawPtr<WorkerThreadStartupData>);
-
     WorkerObjectProxy& m_workerObjectProxy;
     double m_timeOrigin;
 };