Cancel vibration when frame load is committed.

We currently don't handle subframes in a beautiful way, vibrations initiated in one frame may be cancelled from another frame. The expected behavior is not currently defined in the specification but we have started that discussion: http://lists.w3.org/Archives/Public/public-device-apis/2013Jul/0031.html

BUG=222504

Review URL: https://chromiumcodereview.appspot.com/19641006

git-svn-id: svn://svn.chromium.org/blink/trunk@154674 bbb929c8-8fbe-4397-9dbb-9b2b20218538