[GTK] Toggle buttons visually broken with GTK+ 3.13.7
https://bugs.webkit.org/show_bug.cgi?id=136130

Patch by Michael Catanzaro <mcatanzaro@igalia.com> on 2014-08-24
Reviewed by Martin Robinson.

No new tests. Hopefully covered by existing tests, and our tests only
run with GTK+ 3.6 anyway.

* platform/gtk/RenderThemeGtk3.cpp:
(WebCore::paintToggle): use GTK_STATE_FLAG_CHECKED when compiling for
GTK+ 3.13.7 and above to ensure toggle buttons display as toggled.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@172896 268f45cc-cd09-0410-ab3c-d52691b4dbfc