Fire null Device Motion events only once.

Source/modules/device_orientation/NewDeviceOrientationController.cpp

Index: Source/modules/device_orientation/NewDeviceOrientationController.cpp
diff --git a/Source/modules/device_orientation/NewDeviceOrientationController.cpp b/Source/modules/device_orientation/NewDeviceOrientationController.cpp
index 3cf3197694528942473a2ab27e6856b88a34a9ed..b1cf62c300c8b104a7de1bcee45ef3c0575f5745 100644
--- a/Source/modules/device_orientation/NewDeviceOrientationController.cpp
+++ b/Source/modules/device_orientation/NewDeviceOrientationController.cpp
@@ -28,6 +28,7 @@
 #include "modules/device_orientation/NewDeviceOrientationController.h"
 
 #include "core/dom/Document.h"
+#include "modules/device_orientation/DeviceOrientationData.h"
 #include "modules/device_orientation/DeviceOrientationDispatcher.h"
 #include "modules/device_orientation/DeviceOrientationEvent.h"
 
@@ -83,4 +84,11 @@ void NewDeviceOrientationController::unregisterWithDispatcher()
     DeviceOrientationDispatcher::instance().removeDeviceOrientationController(this);
 }
 
+bool NewDeviceOrientationController::isNullEvent(Event* event)
+{
+    ASSERT(event->type() == eventNames().devicemotionEvent);
+    DeviceOrientationEvent* orientationEvent = static_cast<DeviceOrientationEvent*>(event);
+    return !orientationEvent->orientation()->canProvideEventData();
+}
+
 } // namespace WebCore