Will be set when --all is passed to git-cl presubmit to execute
presubmit checks over all files on a repo.

Bug: 1042324
Change-Id: I2ebb7c3ec633f9d3a3774314799aa056bc2919c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2003071Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>