[CSSRegions]Add support for background-color in region styling

[CSSRegions]Add support for background-color in region styling
https://bugs.webkit.org/show_bug.cgi?id=71488

Reviewed by David Hyatt.

Source/WebCore:

This patch enables region styling again. The region styling tests were also added back.
With the improvements from https://bugs.webkit.org/show_bug.cgi?id=76265, hopefully we will not see the same 3% regressions
in performance.

* rendering/RenderObject.h:
(WebCore::RenderObject::style):

LayoutTests:

Add back the region styling tests.

* platform/mac-snowleopard/Skipped:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105426 268f45cc-cd09-0410-ab3c-d52691b4dbfc