Add DepotToolsClient to implement the OwnersClient API
for Depot Tools, and implement the ListOwnersForFile method.

Change-Id: I933a262898439d879c919d695aa62d7702b4c9a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2530509
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>