presubmit: Allow Bot-Commit+1 to self-approve change.

Change-Id: I29a7aeb6f797be015f29e1e514bbe44988a1221e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2775839
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Jason Clinton <jclinton@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

presubmit_canned_checks.py

@@ -1184,7 +1184,8 @@ def CheckOwners(
           ('\n    '.join(suggested_owners))))
     return output_list
 
-  if input_api.is_committing and not reviewers:
+  if (input_api.is_committing and not reviewers and
+      not input_api.gerrit.IsBotCommitApproved(input_api.change.issue)):
     return [output_fn('Missing LGTM from someone other than %s' % owner_email)]
   return []
 

presubmit_support.py

@@ -446,6 +446,9 @@ class GerritAccessor(object):
     return [v for v in label_info.get('all', [])
             if v.get('value', 0) == max_value]
 
+  def IsBotCommitApproved(self, issue):
+    return bool(self._GetApproversForLabel(issue, 'Bot-Commit'))
+
   def IsOwnersOverrideApproved(self, issue):
     return bool(self._GetApproversForLabel(issue, 'Owners-Override'))