Use gesture events to clear active state instead of
synthetic mouse ones.

Note: This changes touch release behaviour to keep hover,
affecting GestureTap and GestureTapDownCancel. Previously,
a touch release would clear the active/hover chain,
setting the element back to default.

This would affect scrolling slightly in that if a finger
lingers a bit before scrolling, the element would be
activated momentarily and then stay hovered for
(and after) the scroll.

BUG=312804, 307670

Review URL: https://codereview.chromium.org/107613002

git-svn-id: svn://svn.chromium.org/blink/trunk@163816 bbb929c8-8fbe-4397-9dbb-9b2b20218538