Fix bug 4082512 IAE "pointerIndex out of range" while zooming over

flashplayer in browser

Fix an issue where gestures weren't being fully canceled by webkit to
the multitouch detector. This will prevent ScaleGestureDetector from
attempting to resume its regularly scheduled gesture already in
progress.

Change-Id: Id4881eeb1df8414dfa23174481bd7dc70fd08fee