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

Source/core/events/BeforeTextInsertedEvent.h

 /*
  * Copyright (C) 2006 Apple Computer, 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 27 matching lines @@
     {
         return adoptRef(new BeforeTextInsertedEvent(text));
     }
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
     virtual bool isBeforeTextInsertedEvent() const OVERRIDE { return true; }
 
     const String& text() const { return m_text; }
     void setText(const String& s) { m_text = s; }
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     explicit BeforeTextInsertedEvent(const String&);
 
     String m_text;
 };
 
 } // namespace
 
 #endif