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

Source/core/loader/FrameLoader.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) Research In Motion Limited 2009. All rights reserved.
  * Copyright (C) 2011 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:
  *
@@ skipping 129 matching lines @@
 
     void didExplicitOpen();
 
     // Callbacks from DocumentWriter
     void didBeginDocument(bool dispatchWindowObjectAvailable);
 
     void receivedFirstData();
 
     String userAgent(const KURL&) const;
 
-    void dispatchDidClearWindowObjectInWorld(DOMWrapperWorld&);
+    void dispatchDidClearWindowObjectInWorld(DOMWrapperWorld*);
     void dispatchDidClearWindowObjectsInAllWorlds();
     void dispatchDocumentElementAvailable();
 
     // The following sandbox flags will be forced, regardless of changes to
     // the sandbox attribute of any parent frames.
     void forceSandboxFlags(SandboxFlags flags) { m_forcedSandboxFlags |= flags; }
     SandboxFlags effectiveSandboxFlags() const;
 
     LocalFrame* opener();
     void setOpener(LocalFrame*);
@@ skipping 121 matching lines @@
 
     bool m_didAccessInitialDocument;
     Timer<FrameLoader> m_didAccessInitialDocumentTimer;
 
     SandboxFlags m_forcedSandboxFlags;
 };
 
 } // namespace WebCore
 
 #endif // FrameLoader_h