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

Source/core/events/OverflowEvent.h

 /*
  * Copyright (C) 2006, 2007, 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 47 matching lines @@
     {
         return adoptRef(new OverflowEvent(type, initializer));
     }
 
     unsigned short orient() const { return m_orient; }
     bool horizontalOverflow() const { return m_horizontalOverflow; }
     bool verticalOverflow() const { return m_verticalOverflow; }
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     OverflowEvent();
     OverflowEvent(bool horizontalOverflowChanged, bool horizontalOverflow, bool verticalOverflowChanged, bool verticalOverflow);
     OverflowEvent(const AtomicString&, const OverflowEventInit&);
 
     unsigned short m_orient;
     bool m_horizontalOverflow;
     bool m_verticalOverflow;
 };
 
 }
 
 #endif // OverflowEvent_h