- It uses a different commit subject than recipe roller.
- Switch from looking up for magic strings to use a regexp instead. Document the
  source of each string, to help keep up when the source diverge.

Tested manually.

Change-Id: I76fc6b6692508c615a0e76c4b6b403f8c513dd31
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1564938
Commit-Queue: Marc-Antoine Ruel <maruel@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>