Fix bugs in clip parent calculations

Fix bugs in clip parent calculations

I noticed two bugs in the clip parent code - when walking up the layers
in the stacking tree looking for clipping layers, I'd forgotten to
consider the layers themselves (I'd only considered their clipping
containers). I'd also incorrectly gated promotion for having a clip
parent on having an ancestor scrolling layer that needed composited
scrolling. This condition was bogus: we often need a clip parent
precisely because we have no ancestor scrolling layer (eg, we're fixed
positioned and have 'escaped' our ancestor scrollers in tree order).

BUG=None

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178649

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178749

[abarth-chromium, 2014-07-22 05:54:11]

lgtm

[commit-bot: I haz the power, 2014-07-22 05:55:06]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/vollick@chromium.org/402283003/1

[commit-bot: I haz the power, 2014-07-22 06:37:09]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/18119)

[commit-bot: I haz the power, 2014-07-22 07:13:44]

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

[commit-bot: I haz the power, 2014-07-22 07:13:45]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/18130)

[Ian Vollick, 2014-07-22 12:46:24]

The CQ bit was checked by vollick@chromium.org

[commit-bot: I haz the power, 2014-07-22 12:47:51]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/vollick@chromium.org/402283003/1

[commit-bot: I haz the power, 2014-07-22 13:26:39]

Change committed as 178649

[johnme, 2014-07-22 15:06:02]

A revert of this CL has been created in
https://codereview.chromium.org/410683002/ by johnme@chromium.org.

The reason for reverting is: non-reparented-overlay-scrollbars.html fails on the
following bots:

http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.7/builds/...
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.8/builds/...
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.8%20%28re....

[Ian Vollick, 2014-07-23 04:07:03]

On 2014/07/22 15:06:02, johnme wrote:
> A revert of this CL has been created in
> https://codereview.chromium.org/410683002/ by mailto:johnme@chromium.org.
> 
> The reason for reverting is: non-reparented-overlay-scrollbars.html fails on
the
> following bots:
> 
>
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.7/builds/...
>
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.8/builds/...
>
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.8%20%28re....

The failures on these bots should be fixed by r284773. I've confirmed on a
retina mac that this test now passes. It looks like the bots are using chromium
at or beyond r284840, so we should be good now. I'm going to put this back in
the cq.

[Ian Vollick, 2014-07-23 04:07:13]

The CQ bit was checked by vollick@chromium.org

[commit-bot: I haz the power, 2014-07-23 04:08:44]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/vollick@chromium.org/402283003/20001

[commit-bot: I haz the power, 2014-07-23 05:09:19]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/18439)

[commit-bot: I haz the power, 2014-07-23 06:12:35]

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

[commit-bot: I haz the power, 2014-07-23 06:12:36]

Try jobs failed on following builders:
  win_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu_triggered...)

[Ian Vollick, 2014-07-23 11:08:20]

The CQ bit was checked by vollick@chromium.org

[commit-bot: I haz the power, 2014-07-23 11:08:56]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/vollick@chromium.org/402283003/20001

[commit-bot: I haz the power, 2014-07-23 11:09:45]

Change committed as 178749