Sync the DeviceOrientation and DeviceMotion interfaces with the spec

third_party/WebKit/Source/modules/device_orientation/DeviceRotationRate.idl

 /*
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+// http://w3c.github.io/deviceorientation/spec-source-orientation.html#devicemotion
+
 [
     GarbageCollected,
     NoInterfaceObject
 ] interface DeviceRotationRate {
     readonly attribute double? alpha;
     readonly attribute double? beta;
     readonly attribute double? gamma;
 };