Fire null Device Motion events only once.

Source/modules/device_orientation/DeviceMotionController.cpp

 /*
  * Copyright 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Samsung Electronics. 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 copyright
@@ skipping 10 matching lines @@
  * 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.
  */
 
 #include "config.h"
 #include "modules/device_orientation/DeviceMotionController.h"
 
 #include "core/dom/Document.h"
+#include "modules/device_orientation/DeviceMotionData.h"
 #include "modules/device_orientation/DeviceMotionDispatcher.h"
 #include "modules/device_orientation/DeviceMotionEvent.h"
 
 namespace WebCore {
 
 DeviceMotionController::DeviceMotionController(Document* document)
     : DeviceSensorEventController(document)
 {
 }
 
@@ skipping 34 matching lines @@
 void DeviceMotionController::registerWithDispatcher()
 {
     DeviceMotionDispatcher::instance().addDeviceMotionController(this);
 }
 
 void DeviceMotionController::unregisterWithDispatcher()
 {
     DeviceMotionDispatcher::instance().removeDeviceMotionController(this);
 }
 
+bool DeviceMotionController::isNullEvent(Event* event)
+{
+    ASSERT(event->type() == eventNames().devicemotionEvent);
+    DeviceMotionEvent* motionEvent = static_cast<DeviceMotionEvent*>(event);
+    return !motionEvent->deviceMotionData()->canProvideEventData();
+}
+
 } // namespace WebCore