[Temp] Add test interface for device motion/orientation.

This change is cherry-picked from upstream revision 225702
(https://src.chromium.org/viewvc/chrome?view=rev&revision=225702).
Crosswalk needs this interface to implement device orientation
API (http://www.w3.org/TR/orientation-event/).

BUG=https://code.google.com/p/chromium/issues/detail?id=261165