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

Source/modules/webmidi/MIDIConnectionEvent.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 48 matching lines @@
 
     static PassRefPtr<MIDIConnectionEvent> create(const AtomicString& type, const MIDIConnectionEventInit& initializer)
     {
         return adoptRef(new MIDIConnectionEvent(type, initializer));
     }
 
     RefPtr<MIDIPort> port() { return m_port; }
 
     virtual const AtomicString& interfaceName() const OVERRIDE { return EventNames::MIDIConnectionEvent; }
 
+    virtual void trace(Visitor* visitor) OVERRIDE { Event::trace(visitor); }
+
 private:
     MIDIConnectionEvent()
     {
         ScriptWrappable::init(this);
     }
 
     MIDIConnectionEvent(const AtomicString& type, PassRefPtr<MIDIPort> port)
         : Event(type, false, false)
         , m_port(port)
     {
         ScriptWrappable::init(this);
     }
 
     MIDIConnectionEvent(const AtomicString& type, const MIDIConnectionEventInit& initializer)
         : Event(type, initializer)
         , m_port(initializer.port)
     {
         ScriptWrappable::init(this);
     }
 
     RefPtr<MIDIPort> m_port;
 };
 
 } // namespace WebCore
 
 #endif // MIDIConnectionEvent_h