On the following tests, WebKitTestRunner goes crazy, using more than 100% CPU apparently handling a flood of mach messages:
Created attachment 61634 [details]
Sample of WebKitTestRunner
Attached a sample of WebKitTestRunner while it is in this spinning state. This is easily reproducible running WebKitTestRunner on one of the tests by hand.
Created attachment 61691 [details]
Committed r63442: <http://trac.webkit.org/changeset/63442>