Change DeviceMotionEvent's DeviceRotationRate to use degrees

The DeviceMotionEvent spec:
https://w3c.github.io/deviceorientation/spec-source-orientation.html#devicemotion
says the DeviceMotionEvent's DeviceRotationRate "must be expressed in
degrees per second (deg/s)". This CL changes the implementation to be
the same as the spec.

Related post and discussion at blink-dev:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/ple1o7bFqEs

Bug: 541607
Change-Id: I8cd5a8fadeebf49deb1126685d267495da7b4c3c
Reviewed-on: https://chromium-review.googlesource.com/658330
Commit-Queue: Jun Cai <juncai@chromium.org>
Reviewed-by: Tim Volodine <timvolodine@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530549}
4 files changed