Make WebWidget::compositeAndReadbackAsync() return void.

Make WebWidget::compositeAndReadbackAsync() return void.

This method returns false when isAcceleratedCompositingActive() is
not enabled. In the future this will always be enabled (at least for
callers of the compositeAndReadbackAsync() method), so having to
support a branch and NOTREACHED() at each call site it awkward.

Instead make this method ASSSERT(isAcceleratedCompositingActive()) and
not return a value.

R=abarth
BUG=251960
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173572

[abarth-chromium, 2014-05-05 22:38:22]

lgtm

[danakj, 2014-05-07 21:40:23]

The CQ bit was checked by danakj@chromium.org

[danakj, 2014-05-07 21:40:35]

The CQ bit was unchecked by danakj@chromium.org

[commit-bot: I haz the power, 2014-05-07 21:40:57]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/danakj@chromium.org/263253002/1

[danakj, 2014-05-07 22:06:19]

The CQ bit was checked by danakj@chromium.org

[commit-bot: I haz the power, 2014-05-07 22:06:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/danakj@chromium.org/263253002/20001

[commit-bot: I haz the power, 2014-05-07 23:12:59]

Change committed as 173572