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

Source/modules/speech/SpeechSynthesisEvent.h

 /*
  * Copyright (C) 2013 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 24 matching lines @@
 public:
     static PassRefPtr<SpeechSynthesisEvent> create();
     static PassRefPtr<SpeechSynthesisEvent> create(const AtomicString& type, unsigned long charIndex, float elapsedTime, const String& name);
 
     unsigned long charIndex() const { return m_charIndex; }
     float elapsedTime() const { return m_elapsedTime; }
     const String& name() const { return m_name; }
 
     virtual const AtomicString& interfaceName() const OVERRIDE { return EventNames::SpeechSynthesisEvent; }
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     SpeechSynthesisEvent();
     SpeechSynthesisEvent(const AtomicString& type, unsigned long charIndex, float elapsedTime, const String& name);
 
     unsigned long m_charIndex;
     float m_elapsedTime;
     String m_name;
 };
 
 } // namespace WebCore
 
 #endif // SpeechSynthesisEvent_h