Make Event RefCountedGarbageCollected and implement trace() methods to the Event hierarcy

Source/core/events/ClipboardEvent.h

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 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.
@@ skipping 23 matching lines @@
     public:
         virtual ~ClipboardEvent();
 
         static PassRefPtr<ClipboardEvent> create(const AtomicString& type, bool canBubbleArg, bool cancelableArg, PassRefPtrWillBeRawPtr<Clipboard> clipboardArg)
         {
             return adoptRef(new ClipboardEvent(type, canBubbleArg, cancelableArg, clipboardArg));
         }
 
         Clipboard* clipboard() const { return m_clipboard.get(); }
 
+        virtual void trace(Visitor*) OVERRIDE;
+
     private:
         ClipboardEvent();
         ClipboardEvent(const AtomicString& type, bool canBubbleArg, bool cancelableArg, PassRefPtrWillBeRawPtr<Clipboard>);
 
         virtual const AtomicString& interfaceName() const OVERRIDE;
         virtual bool isClipboardEvent() const OVERRIDE;
 
-        RefPtrWillBePersistent<Clipboard> m_clipboard;
+        RefPtrWillBeMember<Clipboard> m_clipboard;
     };
 
 } // namespace WebCore
 
 #endif // ClipboardEvent_h