Add a utility method to check approval status for files
when no change has been created yet.

Change-Id: I4cc47e2f598cedc7b7aab68bed356bd3ae566cc0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2551373
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>