Remove wrong overload.

Source/core/dom/MainThreadTaskRunnerTest.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 34 matching lines @@
     virtual bool enqueueEvent(PassRefPtr<Event>) OVERRIDE { return true; }
     virtual bool cancelEvent(Event*) OVERRIDE { return true; }
     virtual void close() OVERRIDE { }
 };
 
 class NullExecutionContext : public ExecutionContext, public RefCounted<NullExecutionContext> {
 public:
     using RefCounted<NullExecutionContext>::ref;
     using RefCounted<NullExecutionContext>::deref;
 
-    virtual void refExecutionContext() OVERRIDE { ref(); }
-    virtual void derefExecutionContext() OVERRIDE { deref(); }
     virtual EventQueue* eventQueue() const OVERRIDE { return m_queue.get(); }
     virtual bool tasksNeedSuspension() { return m_tasksNeedSuspension; }
 
     void setTasksNeedSuspention(bool flag) { m_tasksNeedSuspension = flag; }
 
     NullExecutionContext();
 
 private:
     bool m_tasksNeedSuspension;
     OwnPtr<EventQueue> m_queue;
@@ skipping 63 matching lines @@
     bool isMarked = false;
 
     context->setTasksNeedSuspention(true);
     runner->postTask(MarkingBooleanTask::create(&isMarked));
     runner.clear();
     WebCore::testing::runPendingTasks();
     EXPECT_FALSE(isMarked);
 }
 
 }