Add a function to parse a Gitiles repo URL supporting various edge cases.

R=tandrii@chromium.org

Bug: 877161
Change-Id: Ib4d6a28a2ace2e594f1a4ca31460a446fc6fa052
Reviewed-on: https://chromium-review.googlesource.com/1204914
Commit-Queue: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>