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

Source/core/events/ResourceProgressEvent.h

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 39 matching lines @@
     }
     static PassRefPtr<ResourceProgressEvent> create(const AtomicString& type, bool lengthComputable, unsigned long long loaded, unsigned long long total, const String& url)
     {
         return adoptRef(new ResourceProgressEvent(type, lengthComputable, loaded, total, url));
     }
 
     const String& url() const;
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
+    virtual void trace(Visitor*) OVERRIDE;
+
 protected:
     ResourceProgressEvent();
     ResourceProgressEvent(const AtomicString& type, bool lengthComputable, unsigned long long loaded, unsigned long long total, const String& url);
 
 private:
     String m_url;
 };
 
 } // namespace WebCore
 
 #endif // ResourceProgressEvent_h