I will enable InspectorTest.dumpActivityToSystemConsole and see whether this helps get us more insight into the issue.
<rdar://problem/22383315>
Committed r188766: <http://trac.webkit.org/changeset/188766>
The first log produced: 13:19:41.540 5376 worker/4 inspector/css/modify-rule-selector.html output stderr lines: 13:19:41.540 5376 13:19:41.540 5376 Selector before mutation: .foo 13:19:41.540 5376 Selector after mutation: span.foo 13:19:41.705 5376 worker/4 killing driver 13:19:41.815 5376 worker/4 inspector/css/modify-rule-selector.html failed: 13:19:41.815 5376 worker/4 test timed out 13:19:41.815 5376 worker/4 text diff