Allows for quick retrieval of host and project without having to parse
gerrit_change_repo_url or hard coding.

Bug:
Change-Id: I43f6e0bfda4b54d742bfa7ea20ee781162796608
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2971110
Commit-Queue: Stephanie Kim <kimstephanie@google.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>