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

Source/core/events/BeforeLoadEvent.h

 /*
  * Copyright (C) 2009 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 @@
 
     static PassRefPtr<BeforeLoadEvent> create(const AtomicString& type, const BeforeLoadEventInit& initializer)
     {
         return adoptRef(new BeforeLoadEvent(type, initializer));
     }
 
     const String& url() const { return m_url; }
 
     virtual const AtomicString& interfaceName() const OVERRIDE { return EventNames::BeforeLoadEvent; }
 
+    virtual void trace(Visitor* visitor) OVERRIDE { Event::trace(visitor); }
+
 private:
     BeforeLoadEvent()
     {
         RELEASE_ASSERT(RuntimeEnabledFeatures::beforeLoadEnabled());
         ScriptWrappable::init(this);
     }
 
     explicit BeforeLoadEvent(const String& url)
         : Event(EventTypeNames::beforeload, false, true)
         , m_url(url)
     {
         RELEASE_ASSERT(RuntimeEnabledFeatures::beforeLoadEnabled());
         ScriptWrappable::init(this);
     }
 
     BeforeLoadEvent(const AtomicString& type, const BeforeLoadEventInit& initializer)
         : Event(type, initializer)
         , m_url(initializer.url)
     {
         RELEASE_ASSERT(RuntimeEnabledFeatures::beforeLoadEnabled());
         ScriptWrappable::init(this);
     }
 
     String m_url;
 };
 
 } // namespace WebCore
 
 #endif // BeforeLoadEvent_h