Avoid leaking objects between isolated worlds via attribute event listeners

Source/bindings/v8/V8AbstractEventListener.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 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.
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@@ skipping 91 matching lines @@
         bool hasExistingListenerObject()
         {
             return !m_listener.isEmpty();
         }
 
         void clearListenerObject()
         {
             m_listener.clear();
         }
 
-        DOMWrapperWorld* world() const { return m_world.get(); }
+        virtual DOMWrapperWorld* world() const OVERRIDE FINAL { return m_world.get(); }
 
     protected:
         V8AbstractEventListener(bool isAttribute, PassRefPtr<DOMWrapperWorld>, v8::Isolate*);
 
         virtual void prepareListenerObject(ScriptExecutionContext*) { }
 
         void setListenerObject(v8::Handle<v8::Object> listener);
 
         void invokeEventHandler(ScriptExecutionContext*, Event*, v8::Local<v8::Value> jsEvent);
 
@@ skipping 15 matching lines @@
         // Indicates if this is an HTML type listener.
         bool m_isAttribute;
 
         RefPtr<DOMWrapperWorld> m_world;
         v8::Isolate* m_isolate;
     };
 
 } // namespace WebCore
 
 #endif // V8AbstractEventListener_h