This was important when building crosvm required assembling our own
build tree from lots of different repositories, but now that they've
moved to submodules, it's overly complicated and needlessly
inconsistent with the rest of Nixpkgs.
manifest-versions never seems to contain the release build any more,
so we can't use it to find the version of crosvm being served to CrOS
devices.
Instead, I've changed the update script to take the latest version of
the appropriate crosvm Chrome OS release branch. This is the branch
that gets served. Every release, it is branched off from the
"chromeos" branch (which is the one that passes Chrome OS QA), and
then collects any critical fixes over the lifetime of the release.
With this change, I've introduced a new, simplified versioning
scheme, e.g. 100.0. The tip build is always 1:1 with the Chrome
version, so having both of those is redundant. The other number is
the number of commits that have been added to the release branch after
branching from the chromeos branch, so that the number will go up if
we update to include a new commit from the same release.
The old dashboard no longer exists. Currently, the platform version
being served doesn't exist in manifest versions, but that was also a
problem we had before sometimes.
Otherwise, we might only match a prefix of the version. (Although
it's not likely to be a problem in practice — I doubt we'll end up in
a situation where there's a buildspec number 10x the one we're looking
for.)
crosvm now uses submodules for all of its dependencies to ease
out-of-tree builds, so we no longer need to try to reconstruct a
partial Chromium OS source tree ourselves. Yay!
But, it no longer comes with a Cargo.lock, so we have to bundle that.
"paladin" doesn't seem to be up to date, whereas "full" seems to match
what cros-updates-serving.appspot.com reports is currently being
shipped to Chromebooks.
It has been explained to me that cros-omahaproxy reports which
versions are available to users, while cros-updates-serving reports
the latest builds available for each channel. The latter is probably
better for our use case anyway, and apparently, while both aren't
officially supported, is less likely to randomly break.
So let's use that instead, even if it is much more annoying to parse.
