Use a per-page user gesture token for handling events.

R=abarth@chromium.org
BUG=289648
TEST=fast/events/popup-blocked-from-different-frames.html

Review URL: https://chromiumcodereview.appspot.com/23691053

git-svn-id: svn://svn.chromium.org/blink/trunk@157666 bbb929c8-8fbe-4397-9dbb-9b2b20218538