[Cocoa] Adopt WKWebViewAdditions
Created attachment 264775 [details] Patch
Committed r192013: <http://trac.webkit.org/changeset/192013>
This seems to have broken a few builders. Please check.
Landed speculative build fix in <http://trac.webkit.org/changeset/192029>, and the changelog (whoops) in <https://trac.webkit.org/r192030>