Fire null Device Motion events only once.

Source/modules/device_orientation/DeviceMotionDispatcher.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 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef DeviceMotionDispatcher_h
 #define DeviceMotionDispatcher_h
 
-#include "modules/device_orientation/DeviceMotionData.h"
 #include "modules/device_orientation/DeviceSensorEventDispatcher.h"
 #include "public/platform/WebDeviceMotionListener.h"
 #include "wtf/RefPtr.h"
 
 namespace WebKit {
 class WebDeviceMotionData;
 }
 
 namespace WebCore {
 
@@ skipping 21 matching lines @@
 
     virtual void startListening() OVERRIDE;
     virtual void stopListening() OVERRIDE;
 
     RefPtr<DeviceMotionData> m_lastDeviceMotionData;
 };
 
 } // namespace WebCore
 
 #endif // DeviceMotionDispatcher_h