workers: Move ownership of WebThread from WorkerThread

Source/modules/serviceworkers/ServiceWorkerThread.h

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 26 matching lines @@
 namespace blink {
 
 class WorkerThreadStartupData;
 
 class MODULES_EXPORT ServiceWorkerThread final : public WorkerThread {
 public:
     static PassRefPtr<ServiceWorkerThread> create(PassRefPtr<WorkerLoaderProxy>, WorkerReportingProxy&, PassOwnPtr<WorkerThreadStartupData>);
     virtual ~ServiceWorkerThread();
 
 protected:
-    virtual PassRefPtrWillBeRawPtr<WorkerGlobalScope> createWorkerGlobalScope(PassOwnPtr<WorkerThreadStartupData>) override;
+    PassRefPtrWillBeRawPtr<WorkerGlobalScope> createWorkerGlobalScope(PassOwnPtr<WorkerThreadStartupData>) override;
+    WebThreadSupportingGC& backingThread() override;
 
 private:
     ServiceWorkerThread(PassRefPtr<WorkerLoaderProxy>, WorkerReportingProxy&, PassOwnPtr<WorkerThreadStartupData>);
+
+    OwnPtr<WebThreadSupportingGC> m_thread;
 };
 
 } // namespace blink
 
 #endif // ServiceWorkerThread_h