I'm not sure why exactly this happens, and it's possible that the tests aren't quite right - but there is a less invasive fix for the Java plug-in that we can use for now.
Created attachment 49427 [details] proposed fix
Comment on attachment 49427 [details] proposed fix Can’t DumpRenderTree be modified to use an NSApplication subclass? I don’t think it’s necessary to resort to runtime trickery.
Created attachment 49432 [details] proposed fix
Created attachment 49433 [details] your wish is my command
Committed revision 55200.
This change made DRT run a busyloop while waiting for tests to complete, rather than idling the event loop.
Fixing via bug 119317.