CSS_SELECTORS_LEVEL4 is not enabled on WinCairo. It's already enabled on AppleWin, so I believe it is safe to enable it.
Created attachment 245557 [details] Patch
Yes it is!
Comment on attachment 245557 [details] Patch r=me.
(In reply to comment #2) > Yes it is! Excellent, thanks :)
Comment on attachment 245557 [details] Patch Clearing flags on attachment: 245557 Committed r179277: <http://trac.webkit.org/changeset/179277>
All reviewed patches have been landed. Closing bug.