WebKitTestRunner and WebProcess simultaneously stall in CoreIPC::Connection::sendOutgoingMessage. This can be reproduced running WebKitTestRunner on the following tests:
Both processes appear to be trying to send each other a mach message and are stuck.
Created attachment 61635 [details]
Sample of the Web process
Created attachment 61636 [details]
Sample of the UI process
Created attachment 62025 [details]
Attachment 62025 [details] did not pass style-queue:
Failed to run "['WebKitTools/Scripts/check-webkit-style']" exit_code: 1
WebKit2/Platform/mac/MachUtilities.cpp:26: Found header this file implements before WebCore config.h. Should be: config.h, primary header, blank line, and then alphabetically sorted. [build/include_order] 
Total errors found: 1 in 5 files
If any of these errors are false positives, please file a bug against check-webkit-style.
Committed r63708: <http://trac.webkit.org/changeset/63708>