RenderLayerScrollableArea::updateScrollCornerStyle shouldn't do work if we're using overlay scrollb…

RenderLayerScrollableArea::updateScrollCornerStyle shouldn't do work if we're using overlay scrollbars

This function showed up on a profile of updateStyle in Silk's toggle_drawer
test case, but there no reason to update the scroll corner style if we're using
overlay scrollbars. If the author has created a custom scrollbar, we'll realize
that we don't have overlay scrollbars.

R=esprehn@chromium.org
BUG=335703
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168601

[esprehn, 2014-03-05 23:54:01]

lgtm

[ojan, 2014-03-06 00:35:12]

The CQ bit was checked by ojan@chromium.org

[commit-bot: I haz the power, 2014-03-06 00:35:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/abarth@chromium.org/178903004/20001

[commit-bot: I haz the power, 2014-03-06 01:09:38]

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

[commit-bot: I haz the power, 2014-03-06 01:09:38]

Try jobs failed on following builders: mac_blink_rel

[abarth-chromium, 2014-03-06 01:15:11]

The CQ bit was checked by abarth@chromium.org

[abarth-chromium, 2014-03-06 01:15:41]

The CQ bit was unchecked by abarth@chromium.org

[commit-bot: I haz the power, 2014-03-06 01:15:51]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/abarth@chromium.org/178903004/20001

[abarth-chromium, 2014-03-06 01:54:38]

The test was failing due to scroll bars that appear during layout.  This CL
updates the scroll corner after layout if we've created scrollbars.  It's
slightly gross but it should be safe.

[abarth-chromium, 2014-03-06 01:54:41]

The CQ bit was checked by abarth@chromium.org

[commit-bot: I haz the power, 2014-03-06 01:55:12]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/abarth@chromium.org/178903004/40001

[commit-bot: I haz the power, 2014-03-06 08:24:39]

Change committed as 168601