The new message lets us know which directory is involved and what we can
do to fix it.

Bug: 
Change-Id: Icfcb92b35b1ef2644649789b1e8473cb6ae50336
Reviewed-on: https://chromium-review.googlesource.com/571702Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46659}