Revert of Make DOMWrapperWorld::current() return a reference instead of a pointer

Source/core/events/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
@@ skipping 26 matching lines @@
             CPPEventListenerType,
             ConditionEventListenerType,
             NativeEventListenerType,
         };
 
         virtual ~EventListener() { }
         virtual bool operator==(const EventListener&) = 0;
         virtual void handleEvent(ExecutionContext*, Event*) = 0;
         virtual bool wasCreatedFromMarkup() const { return false; }
         virtual bool belongsToTheCurrentWorld() 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