Reduce repetitive EventTarget subclassing

Source/core/svg/SVGElementInstance.h

Index: Source/core/svg/SVGElementInstance.h
diff --git a/Source/core/svg/SVGElementInstance.h b/Source/core/svg/SVGElementInstance.h
index 1008087daf43f0e61eea3ea4967cda48476f5517..8a143d49b27f7887e045688c9d2d333cb2cac9d7 100644
--- a/Source/core/svg/SVGElementInstance.h
+++ b/Source/core/svg/SVGElementInstance.h
@@ -174,10 +174,10 @@ private:
     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;