When mirroring b2g repositories to git.mozilla.org, the name of the mirror must meet several criteria. These criteria are mostly understood by a few folks, but that's neither scalable nor "a good thing". The best way to document the criteria is to write a script to generate the path on git.mozilla.org given an upstream URL. That script will be quite reusable for both legacy & new vcs-sync, and may find other uses.
work in progress at https://github.com/hwine/mirror-mapper -- just needs test suite to show it works for all existing repositories.
no longer meaningful in light of bug 1277297