Add missing virtual keyword for methods with OVERRIDE

Source/core/dom/MessagePort.h

 /*
  * Copyright (C) 2008 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 66 matching lines @@
     // Returns 0 if there is an exception, or if the passed-in array is 0/empty.
     static PassOwnPtr<MessagePortChannelArray> disentanglePorts(const MessagePortArray*, ExceptionState&);
 
     // Returns 0 if the passed array is 0/empty.
     static PassOwnPtr<MessagePortArray> entanglePorts(ExecutionContext&, PassOwnPtr<MessagePortChannelArray>);
 
     bool started() const { return m_started; }
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
     virtual ExecutionContext* executionContext() const OVERRIDE { return ActiveDOMObject::executionContext(); }
-    MessagePort* toMessagePort() OVERRIDE { return this; }
+    virtual MessagePort* toMessagePort() OVERRIDE { return this; }
 
     // ActiveDOMObject implementation.
     virtual bool hasPendingActivity() const OVERRIDE;
     virtual void stop() OVERRIDE { close(); }
 
     void setOnmessage(PassRefPtr<EventListener> listener, DOMWrapperWorld* world)
     {
         setAttributeEventListener(EventTypeNames::message, listener, world);
         start();
     }
@@ skipping 16 matching lines @@
 
     bool m_started;
     bool m_closed;
 
     WeakPtrFactory<MessagePort> m_weakFactory;
 };
 
 } // namespace WebCore
 
 #endif // MessagePort_h