We may need to submit a chain of CLs. With this sub-cmd, we could
track their revisions along the chain, without querying them one
by one.

BUG=1236658
TEST=local run

Change-Id: If5930fb8f01daccff4d7c5c5e91c8db8887d8e47
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3098095Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Michael Moss <mmoss@chromium.org>
Commit-Queue: Xinan Lin <linxinan@chromium.org>