pre-upload: require use-manifests=strict for new repos

We don't want people to add new repos w/out manifests, so make it a
presubmit failure.

BUG=chromium:207003
TEST=unittests pass

Change-Id: Id241b0faad7a569dfeb471119952c770e2058021
Reviewed-on: https://chromium-review.googlesource.com/312390
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Bernie Thompson <bhthompson@chromium.org>
2 files changed