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

Source/modules/device_orientation/DeviceMotionEvent.cpp

 /*
  * Copyright (C) 2010 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 92 matching lines @@
 
     isNull = true;
     return 0;
 }
 
 const AtomicString& DeviceMotionEvent::interfaceName() const
 {
     return EventNames::DeviceMotionEvent;
 }
 
+void DeviceMotionEvent::trace(Visitor* visitor)
+{
+    visitor->trace(m_deviceMotionData);
+    visitor->trace(m_acceleration);
+    visitor->trace(m_accelerationIncludingGravity);
+    visitor->trace(m_rotationRate);
+    Event::trace(visitor);
+}
+
 } // namespace WebCore