Long term plan is to separate GitDependency and CipdDependency,
where most of the current Dependency code is moved to GitDependency,
since it's not relevant to Cipd anyway.

Bug: 839925
Change-Id: Ic238a24fa7add302704934f79004e8a9ca886895
Reviewed-on: https://chromium-review.googlesource.com/1044651
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>