I'm still seeing this assertion, e.g. here: <http://build.webkit.org/results/Apple%20MountainLion%20Debug%20WK2%20(Tests)/r155994%20(12664)/compositing/geometry/clipping-foreground-crash-log.txt>. The test is quite flaky on bots too: <http://webkit-test-results.appspot.com/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=compositing%2Fgeometry%2Fclipping-foreground.html>. Not sure if it's just this one test, or multiple.