Cleanup: Add toDeviceMotionEvent and toDeviceOrientationEvent.

Source/modules/device_orientation/DeviceMotionEvent.h

 /*
  * 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 50 matching lines @@
     DeviceMotionEvent();
     DeviceMotionEvent(const AtomicString& eventType, DeviceMotionData*);
 
     RefPtr<DeviceMotionData> m_deviceMotionData;
 
     RefPtr<DeviceAcceleration> m_acceleration;
     RefPtr<DeviceAcceleration> m_accelerationIncludingGravity;
     RefPtr<DeviceRotationRate> m_rotationRate;
 };
 
+inline DeviceMotionEvent* toDeviceMotionEvent(Event* event)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!event || event->interfaceName() == EventNames::DeviceMotionEvent);
+    return static_cast<DeviceMotionEvent*>(event);
+}
+
 } // namespace WebCore
 
 #endif // DeviceMotionEvent_h