Needed by Skia's PostUploadHooks, so that presubmit_support doesn't
depend on git-cl internal classes.

Bug: 1042324
Change-Id: If8f4e6ea035197667cd9705a4274590c4d11511e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2007670Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>