Re-land fixes format always saying the folder was dirty.

The --full option would skip setting the return value of the format
command when used with --dry-run. This in turn would cause the
presubmit check to always pass when --full was enabled in a repo by
default.

Was discovered in the ANGLE repository.

Bug: angleproject:4241
Change-Id: I986646336d1857af2826863ef4becbf2b9ee3049
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1993910
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>