Enable the Vibration API in stable.

The approved intent to implement and ship is here:
https://groups.google.com/a/chromium.org/forum/#!searchin/blink-dev/vibration$20api/blink-dev/hH9bJGWKAbk/AFPov-g5VMMJ

BUG=222504

Review URL: https://codereview.chromium.org/34923002

git-svn-id: svn://svn.chromium.org/blink/trunk@160711 bbb929c8-8fbe-4397-9dbb-9b2b20218538