Implement WTF::WeakPtr in terms of base::WeakPtr

third_party/WebKit/Source/core/dom/MainThreadTaskRunner.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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 56 matching lines @@
 
     void postTaskInternal(const WebTraceLocation&, std::unique_ptr<ExecutionContextTask>, bool isInspectorTask, bool instrumenting);
 
     // Untraced back reference to the owner Document;
     // this object has identical lifetime to it.
     UntracedMember<ExecutionContext> m_context;
     Timer<MainThreadTaskRunner> m_pendingTasksTimer;
     Vector<std::pair<std::unique_ptr<ExecutionContextTask>, bool /* instrumenting */>> m_pendingTasks;
     bool m_suspended;
     WeakPtrFactory<MainThreadTaskRunner> m_weakFactory;
+    WeakPtr<MainThreadTaskRunner> m_weakPtr;
 };
 
 inline std::unique_ptr<MainThreadTaskRunner> MainThreadTaskRunner::create(ExecutionContext* context)
 {
     return wrapUnique(new MainThreadTaskRunner(context));
 }
 
 } // namespace blink
 
 #endif