For windows testing, we will need to run some test suites with signed artifacts. (at least browser-chrome and xpcshell) To facilitate future potential needs for this, we should wire it up to the taskgraph in an easy way to specify that a test depends on signed bits, but not necessarily require it of all tests, to speed up initial testing start time. This will be part of the work for on-change signing.

The method was added as part of bug 1374589.