Take MT jank into account when animating the scroll offset on CC

This CL calculates the jank by subtracting base::TimeTicks::Now from
the event platform time when GestureScrollUpdate is called.

BUG=616995
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2040543002
Cr-Commit-Position: refs/heads/master@{#416561}
17 files changed