Reduce repetitive EventTarget subclassing

Source/core/svg/SVGElementInstance.h

 /*
  * Copyright (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2011 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 156 matching lines @@
     friend void Private::addChildNodesToDeletionQueue(GenericNode*& head, GenericNode*& tail, GenericNodeContainer* container);
 
     bool hasChildNodes() const { return m_firstChild; }
 
     void setFirstChild(SVGElementInstance* child) { m_firstChild = child; }
     void setLastChild(SVGElementInstance* child) { m_lastChild = child; }
 
     void setNextSibling(SVGElementInstance* sibling) { m_nextSibling = sibling; }
     void setPreviousSibling(SVGElementInstance* sibling) { m_previousSibling = sibling; }
 
-    virtual void refEventTarget() { ref(); }
-    virtual void derefEventTarget() { deref(); }
-    virtual EventTargetData* eventTargetData();
-    virtual EventTargetData* ensureEventTargetData();
+    virtual void refEventTarget() OVERRIDE { ref(); }
+    virtual void derefEventTarget() OVERRIDE { deref(); }
+    virtual EventTargetData* eventTargetData() OVERRIDE;
+    virtual EventTargetData& ensureEventTargetData() OVERRIDE;
 
     SVGElementInstance* m_parentInstance;
 
     SVGUseElement* m_correspondingUseElement;
     SVGUseElement* m_directUseElement;
     RefPtr<SVGElement> m_element;
     RefPtr<SVGElement> m_shadowTreeElement;
 
     SVGElementInstance* m_previousSibling;
     SVGElementInstance* m_nextSibling;
 
     SVGElementInstance* m_firstChild;
     SVGElementInstance* m_lastChild;
 };
 
 } // namespace WebCore
 
 #endif