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

Source/core/events/ResourceProgressEvent.cpp

 /*
  * 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 33 matching lines @@
 const String& ResourceProgressEvent::url() const
 {
     return m_url;
 }
 
 const AtomicString& ResourceProgressEvent::interfaceName() const
 {
     return EventNames::ResourceProgressEvent;
 }
 
+void ResourceProgressEvent::trace(Visitor* visitor)
+{
+    ProgressEvent::trace(visitor);
 }
+
+}