By using SelectorQuery in Element::webkitMatchesSelector(), we can not only simplify the code but also improve the performance thanks to the cache mechanism of SelectorQuery which was implemented in bug 87942.
Created attachment 145511 [details] Patch
I've found that SelectorDataList::matches() had been used by nobody before this patch:)
Comment on attachment 145511 [details] Patch r=me
Comment on attachment 145511 [details] Patch Clearing flags on attachment: 145511 Committed r119375: <http://trac.webkit.org/changeset/119375>
All reviewed patches have been landed. Closing bug.