GitLab

GestureTapDown events are always handled by the WK thread. They are
frequently followed by a GestureScrollStart which can be handled on the
compositor thread. In this case, the GTD event is unnecessary and its only
side effect is to make the compositor thread block on the WK thread. This
makes touchscreen scrolling sluggish if the WK thread is busy.

This change defers sending the GTD briefly so that it can be suppressed
if the GTD event is part of a scroll gesture. This increases the likelyhood
that a scroll gesture can be successfully handled on the compositor thread.

BUG=137555
TESTS= by hand, by unit test.


Review URL: https://chromiumcodereview.appspot.com/10855200

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@152230 0039d316-1c4b-4281-b951-d872f2087c98