Reland "Implement async touchmove dispatch during scroll"

Reland "Implement async touchmove dispatch during scroll"

The patch landed originally in r266470, but was reverted in r266579 due to an
uninitialized variable.  The fix was reviewed in crrev.com/253813003.

This implements a touch dispatch model in which touchmove sending is throttled
while a scroll sequence is active and being consumed. Such touchmove's are
marked with |cancelable = false|, indicating to any potential consumers that the
event cannot be prevented from triggering a platform gesture. Throttling limits
the touchmove sending rate during scrolling to 1 event per 200ms.

BUG=346693, 367692
NOTRY=true
TBR=jochen@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266585

[jdduke (slow), 2014-04-28 16:06:27]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2014-04-28 16:06:54]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jdduke@chromium.org/254803012/1

[commit-bot: I haz the power, 2014-04-28 16:15:54]

Change committed as 266585