perf/document-contains.html fails occasionally on win. This seems distinct from the timeout/slowness mentioned in bug 71652. Arv, assigning to you for investigation simply because you are the last to touch the test.
For now I'm going to mark it flaky.
Created attachment 115136 [details]
Committed r100263: <http://trac.webkit.org/changeset/100263>
Marked as SLOW only as of http://trac.webkit.org/changeset/109420
Looks like it's no longer slow.