The GMP manager uses a copy of the update service's url formatting code and has
since fallen out of sync. We'll also want to use the same formatting code for
the system add-on update checks so this just exposes it in a shared API.
I've moved the contents of UpdateChannel.jsm to UpdateUtils.jsm and exposed
formatUpdateURL there as well as a few properties that the update service still
needs access to.
UpdateUtils.UpdateChannel is intended to be a lazy getter but isn't for now
since tests expect to be able to change the update channel at runtime.
--HG--
extra : commitid : KsbH21csjH4
extra : rebase_source : bc7c08de1ec6e802261b8cd294d88ee2c4e75c2d
a22c2d1f9e