Do not let random people CR+1 CR-1

Change-Id: Ic56a5de870b0ed8385046bc348fb289a84b8288b
Reviewed-on: https://boringssl-review.googlesource.com/c/All-Projects/+/72607
Commit-Queue: David Benjamin <davidben@google.com>
Auto-Submit: Bob Beck <bbe@google.com>
Reviewed-by: David Benjamin <davidben@google.com>