The following layout test is flaky on Mac platform/mac-wk2/plugins/mouse-events-scaled.html http://webkit-test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=platform%2Fmac-wk2%2Fplugins%2Fmouse-events-scaled.html
Added test expectation in http://trac.webkit.org/changeset/148362.