It breaks themes using rounded stepper buttons on scrollbars like Adwaita
See gtk+ commit: http://git.gnome.org/browse/gtk+/commit/?id=11f07f9bdcc34861368faa8b54775157bbd0d9e6
Created attachment 84932 [details] Patch
Comment on attachment 84932 [details] Patch Seems sane.
Committed r80555: <http://trac.webkit.org/changeset/80555>