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

Source/core/events/AutocompleteErrorEvent.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:
  * 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 37 matching lines @@
 
     static PassRefPtr<AutocompleteErrorEvent> create(const AtomicString& eventType, const AutocompleteErrorEventInit& initializer)
     {
         return adoptRef(new AutocompleteErrorEvent(eventType, initializer));
     }
 
     const String& reason() const { return m_reason; }
 
     virtual const AtomicString& interfaceName() const OVERRIDE { return EventNames::AutocompleteErrorEvent; }
 
+    virtual void trace(Visitor* visitor) OVERRIDE { Event::trace(visitor); }
+
 private:
     AutocompleteErrorEvent()
     {
         ScriptWrappable::init(this);
     }
 
     AutocompleteErrorEvent(const String& reason)
         : Event(EventTypeNames::autocompleteerror, false, false)
         , m_reason(reason)
     {
         ScriptWrappable::init(this);
     }
 
     AutocompleteErrorEvent(const AtomicString& eventType, const AutocompleteErrorEventInit& initializer)
         : Event(eventType, initializer)
         , m_reason(initializer.reason)
     {
         ScriptWrappable::init(this);
     }
 
     String m_reason;
 };
 
 } // namespace WebCore
 
 #endif // AutocompleteErrorEvent_h