It was enabled accidentally by r122175 and it caused build fail on the Qt-win buildbots (Qt 4.8) And then I disabled it again by r122219. If you are interested in enabling 3D_GRAPHICS on Windows, you can find the detailed build error here: https://bugs.webkit.org/show_bug.cgi?id=90850#c2
I'm looking into this one. WK2 doesn't work otherwise :)
Created attachment 163820 [details] Patch
Committed r128435: <http://trac.webkit.org/changeset/128435>