The new API here could support users to update files to remote
repo without loading the source code to the bot.

BUG=1207955
TEST=train

Change-Id: I2970171bf5b58db0db41bab5a433fc6721b7b2aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3042407
Commit-Queue: Xinan Lin <linxinan@chromium.org>
Reviewed-by: Michael Moss <mmoss@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>