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

Source/core/events/WebKitAnimationEvent.h

 /*
  * Copyright (C) 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 44 matching lines @@
         return adoptRef(new WebKitAnimationEvent(type, initializer));
     }
 
     virtual ~WebKitAnimationEvent();
 
     const String& animationName() const;
     double elapsedTime() const;
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     WebKitAnimationEvent();
     WebKitAnimationEvent(const AtomicString& type, const String& animationName, double elapsedTime);
     WebKitAnimationEvent(const AtomicString&, const WebKitAnimationEventInit&);
 
     String m_animationName;
     double m_elapsedTime;
 };
 
 } // namespace WebCore
 
 #endif // WebKitAnimationEvent_h