Re-land r150168 with some OS version guards.

* WebView/WebFrameView.mm:
(-[WebFrameView drawRect:]):
(-[WebFrameView wantsUpdateLayer]):
(-[WebFrameView updateLayer]):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150194 268f45cc-cd09-0410-ab3c-d52691b4dbfc