See http://webkit-test-results.appspot.com/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=fullscreen%2Fanonymous-block-merge-crash.html it times out >30 seconds multiple times per day, only on WebKit1.
http://trac.webkit.org/changeset/159257
http://trac.webkit.org/changeset/159304
This doesn't seem to happen any more, according to flakiness dashboard.