Prolog rules for branch ownership

This CL sets up the plumbing for branch ownership in Chrome OS via the
Branch-Review label. This label is necessary to submit but only shows up
on branches opted-in to branch review via the 'opt_in_branch_review'
predicate. Any CL covered by the 'opt_out_branch_review' predicate will
be excluded from branch review regardless of any opt_in predicates.

BUG=chromium:987022
TEST=Tested in general-sandbox repository in crrev.com/1737138

Change-Id: I107fff7e9d42f47663fbb0435f5bcf538ab25474
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/+/1731533
Tested-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
1 file changed