Allow touch events to be uncancelable

Allow touch events to be uncancelable

The touchevents specification says (http://www.w3.org/TR/touch-events/#list-of-touchevent-types) that touchcancel events should not be cancelable.

We'd also like to allow other touch events (touchmove and touchend) to sometimes be uncancelable (sent async) as well, so rather than special-case touchcancel here we plumb a bit from the browser.  This leaves the decision over which events are cancelable purely in the hands of the browser (except for edge cases around synthetic events), which makes sense because only the browser can know whether it plans to wait for an ACK for the event before proceeding with gesture recognition.

Note that I can't properly test this in a layout test without changing EventSender in the chromium repo, but I can't change EventSender until WebTouchEvent has changed.  So there's no avoiding a 3-sided patch here.  Once the first 2 CLs have landed I'll land a new LayoutTest before marking bug 365681 as Fixed.

BUG=365681, 361306
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172329

[Rick Byers, 2014-04-22 18:16:12]

Adam, please take a look (this is that change related to touchmove absorption
that we discussed).

Thanks,
   Rick

[abarth-chromium, 2014-04-22 20:40:41]

lgtm

[Rick Byers, 2014-04-22 20:46:07]

The CQ bit was checked by rbyers@chromium.org

[commit-bot: I haz the power, 2014-04-22 20:46:34]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/247483002/30001

[commit-bot: I haz the power, 2014-04-22 21:57:11]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-04-22 21:57:11]

Try jobs failed on following builders:
  tryserver.blink on linux_blink_dbg

[Rick Byers, 2014-04-23 00:11:58]

The CQ bit was checked by rbyers@chromium.org

[commit-bot: I haz the power, 2014-04-23 00:12:18]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/247483002/30001

[commit-bot: I haz the power, 2014-04-23 07:15:12]

Change committed as 172329