Re-enable simple line layout for GTK
https://bugs.webkit.org/show_bug.cgi?id=123388

Reviewed by Andreas Kling.

Source/WebCore: 

* rendering/SimpleLineLayout.cpp:
(WebCore::SimpleLineLayout::canUseFor): 8-bit TextRun support is now enabled for the GTK port, so the port
can use the simple line layout.

Source/WTF: 

* wtf/FeatureDefines.h: Enable the 8-bit TextRun support for the GTK port.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@158102 268f45cc-cd09-0410-ab3c-d52691b4dbfc