Disable scrolling for fullscreen elements by changing scroll layer size.

Disable scrolling for fullscreen elements by changing scroll layer size.

After https://codereview.chromium.org/476113004 CC depends on the
tree structure of scroll/clip layers to determine the viewport size, so
detaching them breaks fullscreen mode.  Switch to the other
approach of changing the scroll layer bounds.

BUG=410452
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181926

[aelias_OOO_until_Jul13, 2014-09-09 22:00:41]

aelias@chromium.org changed reviewers:
+ esprehn@chromium.org

[aelias_OOO_until_Jul13, 2014-09-09 22:04:15]

PTAL.  This changes back to the other approach originally considered in
https://codereview.chromium.org/200943002 because detaching the layer hierarchy
turns out to cause more problems.  I think it's cleanest to set the size to zero
instead of trying to make an exact fit; CC should clamp the scroll properly to
the origin in the zero-size case.

In the long run, I'd like to move this to using setUserScrollable.  But
setUserScrollable is currently no-op: making that work is blocked behind
shipping the new pinch-virtual-viewport stuff.  Since fullscreen video is
totally broken right now, we need to do something in the short term.

[aelias_OOO_until_Jul13, 2014-09-11 03:50:11]

esprehn@ -- nag for review because this came up as a potential dev blocker (this
fixes a bug making fullscreen video unusable).

[esprehn, 2014-09-12 18:14:41]

lgtm

[aelias_OOO_until_Jul13, 2014-09-12 18:18:46]

The CQ bit was checked by aelias@chromium.org

[commit-bot: I haz the power, 2014-09-12 18:19:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/558813003/1

[commit-bot: I haz the power, 2014-09-12 19:40:26]

Committed patchset #1 (id:1) as 181926