Add perf tests for new async touchmove touch event model

Add a test page for scrolling in the presence of empty (or synthetically
delayed) touch handlers in both mobile and desktop (ACK timeout)
versions.  Test it using both a short scroll gesture and a repeating
scroll bounce that hits the scroll limit over and over again within the
same gesture.  This is designed to show that active scrolling is not
impacted by delays on the main thread, but that hitting the scroll limit
now is (but wasn't previously in our touchcancel model).  A bounce back
and forth across the scroll limit on a mobile page with a slow touch
handler is the pathological worst case for our new async touchmove
model, but it should not be a major problem when the handler is fast or
when the touch ACK timeout is enabled.

Discussion of these tests and results comparing async touchmove,
absorption and touchcancel mode are in this thread:
https://groups.google.com/a/chromium.org/forum/#!topic/input-dev/2OkuxHPTdcI

Results/traces are most meaningful when combined with the fixes here:
https://codereview.chromium.org/273523005

BUG=349917

Review URL: https://codereview.chromium.org/232003004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269124 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed