Right now we run regular expressions on the domain every time we have any rules that match with if-domain or unless-domain. This caches the results of running regular expressions on the domain of the main document's url so we only need to run those regular expressions when the main document changes domain.
Created attachment 256536 [details] Patch
Created attachment 256635 [details] Patch
Created attachment 256802 [details] Patch
Created attachment 256809 [details] Patch
I measured this to be about a 25% improvement in interpreting time in one case.
Comment on attachment 256809 [details] Patch lgtm
http://trac.webkit.org/changeset/186912