Optimization strategies for nth are different from other structural pseudo classes (:first-child etc). Move them to a separate test.
Created attachment 331916 [details] patch
Comment on attachment 331916 [details] patch Clearing flags on attachment: 331916 Committed r227347: <https://trac.webkit.org/changeset/227347>
All reviewed patches have been landed. Closing bug.
<rdar://problem/36743864>