This reworks how the Mochitest DOMWINDOW and DOCSHELL leak detector works. Rather than
collecting immediately in the top-level script, it sends a message to all processes
telling them to carry out collections. Each process prints out a message when it has
finished the collections. This message is used by the test harness to decide when windows
and docshells for that process should be have been destroyed.
In non-e10s mode, the shutdown leak detector is only run in the parent process, to work
around various issues with leak detection in the thumbnail process tests.
This reworks how the Mochitest DOMWINDOW and DOCSHELL leak detector works. Rather than
collecting immediately in the top-level script, it sends a message to all processes
telling them to carry out collections. Each process prints out a message when it has
finished the collections. This message is used by the test harness to decide when windows
and docshells for that process should be have been destroyed.
