Fix crash in taking a screenshot of a closed popup

Fix crash in taking a screenshot of a closed popup

You can't assume that there's a root layer always during layout, even if
there's a composite and readback.  WebTestProxyBase::CapturePixelsAsync
iterates through popups (which may get closed between that call and
Layout).  If it's closed, then its root layer goes away.

BUG=470817
Committed: https://crrev.com/cf337a958289161fa9106a51ff5acd19468bcda3
Cr-Commit-Position: refs/heads/master@{#322611}

[enne (OOO), 2015-03-26 23:03:19]

enne@chromium.org changed reviewers:
+ piman@chromium.org

[piman, 2015-03-26 23:09:58]

lgtm

https://codereview.chromium.org/1038133003/diff/1/content/renderer/gpu/render...
File content/renderer/gpu/render_widget_compositor.cc (right):

https://codereview.chromium.org/1038133003/diff/1/content/renderer/gpu/render...
content/renderer/gpu/render_widget_compositor.cc:808:
temporary_copy_output_request_ = nullptr;
nit: wrong indent, or did you forget brackets?
(it doesn't appear to make a functional difference)

[enne (OOO), 2015-03-27 17:40:53]

https://codereview.chromium.org/1038133003/diff/1/content/renderer/gpu/render...
File content/renderer/gpu/render_widget_compositor.cc (right):

https://codereview.chromium.org/1038133003/diff/1/content/renderer/gpu/render...
content/renderer/gpu/render_widget_compositor.cc:808:
temporary_copy_output_request_ = nullptr;
On 2015/03/26 23:09:58, piman (Very slow to review) wrote:
> nit: wrong indent, or did you forget brackets?
> (it doesn't appear to make a functional difference)

Last minute edit; forgot brackets.  <_<

*blush*

[enne (OOO), 2015-03-27 17:41:37]

The CQ bit was checked by enne@chromium.org

[enne (OOO), 2015-03-27 17:41:38]

The patchset sent to the CQ was uploaded after l-g-t-m from piman@chromium.org
Link to the patchset: https://codereview.chromium.org/1038133003/#ps20001
(title: "Add brackets; improve comments")

[commit-bot: I haz the power, 2015-03-27 17:42:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1038133003/20001

[commit-bot: I haz the power, 2015-03-27 18:36:28]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-27 18:38:18]

Patchset 2 (id:??) landed as
https://crrev.com/cf337a958289161fa9106a51ff5acd19468bcda3
Cr-Commit-Position: refs/heads/master@{#322611}