Refactoring WorkletThreadBackingHolder with template pattern

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef AbstractAnimationWorkletThread_h
 #define AbstractAnimationWorkletThread_h
 
 #include "core/workers/WorkerLoaderProxy.h"
 #include "core/workers/WorkerThread.h"
 #include "modules/ModulesExport.h"
 #include <memory>
 
 namespace blink {
 
 class WorkerReportingProxy;
 
 // TODO(ikilpatrick): Remove this class up to AnimationWorkletThread once we no
 // longer have CompositorWorker.
 class MODULES_EXPORT AbstractAnimationWorkletThread : public WorkerThread {
  public:
   ~AbstractAnimationWorkletThread() override;
 
   WorkerBackingThread& workerBackingThread() override;
-  void clearWorkerBackingThread() override {
-    // Do nothing.
-    // The backing thread is cleared by clearSharedBackingThread().
-  }
+
+  // The backing thread is cleared by clearSharedBackingThread().
+  void clearWorkerBackingThread() override {}
 
   bool shouldAttachThreadDebugger() const override { return false; }
 
+  // This may block the main thread.
   static void collectAllGarbage();
 
   static void ensureSharedBackingThread();
+  static void clearSharedBackingThread();
+
   static void createSharedBackingThreadForTest();
 
-  static void clearSharedBackingThread();
-
  protected:
   AbstractAnimationWorkletThread(PassRefPtr<WorkerLoaderProxy>,
                                  WorkerReportingProxy&);
 
   bool isOwningBackingThread() const override { return false; }
 };
 
 }  // namespace blink
 
 #endif  // AbstractAnimationWorkletThread_h