If the option is given, git cl format uses the input diff file to
determine the files and sections to format instead of git-diff.
The intended use case is to remove git dependencies in case
presubmit_support.py is executed with a diff file and it calls
presubmit_canned_checks.CheckPatchFormatted().
Bug: 386840832
Change-Id: Ia1eacd1bdb81731e07753df19ebf1d2470c9f1aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/6912693
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Scott Lee <ddoman@chromium.org>