In order to be able to do offline builds for mobile we need to collect and
distribute Glean dependencies beforehand.[1]

There are three steps involved in the process:
  1) Finding out the `glean_parser` version
  2) Downloading and verifying the dependencies, and creating the tarball
  3) Pushing it to the sources mirror

1)

Running `make list_toolchain_updates-android-components` should tell
you which version of `glean_parser` is needed.

2)

Update `steps/create_glean_deps_tarball/version` in `projects/glean/config`
to the version from step 1 above.

Run this command to generate the tarball:

  make create_glean_deps_tarball

There is no really good way (yet) to verify that `pip` gave us actually what we
wanted. We can download `glean_parser` and its dependencies using a different
network path, though, e.g. by using `torsocks`. Comparing the results of both
downloads should yield the exact same binaries.

If you want to use torsocks, you can use this command:

  make create_glean_deps_tarball-with_torsocks

3)

Upload the compressed tarball to the sources mirror and update the SHA-256 sum of
it as well as the `glean_parser` version in the respective projects.

[1] See: https://bugzilla.mozilla.org/show_bug.cgi?id=1651662 for details.
[2] https://github.com/mozilla/glean