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

Source/core/html/canvas/WebGLContextEvent.h

 /*
  * Copyright (C) 2010 Google 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
@@ skipping 38 matching lines @@
     static PassRefPtr<WebGLContextEvent> create(const AtomicString& type, const WebGLContextEventInit& initializer)
     {
         return adoptRef(new WebGLContextEvent(type, initializer));
     }
     virtual ~WebGLContextEvent();
 
     const String& statusMessage() const { return m_statusMessage; }
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 private:
     WebGLContextEvent();
     WebGLContextEvent(const AtomicString& type, bool canBubble, bool cancelable, const String& statusMessage);
     WebGLContextEvent(const AtomicString&, const WebGLContextEventInit&);
 
     String m_statusMessage;
 };
 
 } // namespace WebCore
 
 #endif // WebGLContextEvent_h