Avoid leaking objects between isolated worlds via attribute event listeners

Source/core/dom/EventListener.h

 /*
  * Copyright (C) 2006, 2008, 2009 Apple Inc. 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,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #ifndef EventListener_h
 #define EventListener_h
 
 #include <wtf/RefCounted.h>
 
 namespace WebCore {
 
+    class DOMWrapperWorld;
+    class Event;
     class ScriptExecutionContext;
-    class Event;
 
     class EventListener : public RefCounted<EventListener> {
     public:
         enum Type {
             JSEventListenerType, 
             ImageEventListenerType, 
             ObjCEventListenerType,
             CPPEventListenerType,
             ConditionEventListenerType,
             GObjectEventListenerType,
             NativeEventListenerType,
             SVGTRefTargetEventListenerType
         };
 
         virtual ~EventListener() { }
         virtual bool operator==(const EventListener&) = 0;
         virtual void handleEvent(ScriptExecutionContext*, Event*) = 0;
         virtual bool wasCreatedFromMarkup() const { return false; }
+        virtual DOMWrapperWorld* world() const { return 0; }
 
         bool isAttribute() const { return virtualisAttribute(); }
         Type type() const { return m_type; }
 
     protected:
         explicit EventListener(Type type)
             : m_type(type)
         {
         }
 
     private:
         virtual bool virtualisAttribute() const { return false; }
         
         Type m_type;
     };
 
 }
 
 #endif