The following layout test is extremely flaky on Mac WK2 bots, especially debug (failing every second or third run): platform/mac-wk2/plugins/slow/asynchronous-plugin-initialization-multiple.html See http://webkit-test-results.appspot.com/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=platform%2Fmac-wk2%2Fplugins%2Fslow%2Fasynchronous-plugin-initialization-multiple.html
http://trac.webkit.org/changeset/159396