code: func EnsurePubSubSubscribed(c context.Context, settings *config.Settings) error {
  	if settings.Buildbucket != nil {
  		c = withClientFactory(c, prodPubSubClientFactory)
  		return ensureBuildbucketSubscribed(c, settings.Buildbucket.Project)
  	}
  	// TODO(hinoka): Ensure buildbot subscribed.
  	return nil
  }
docs: // EnsurePubSubSubscribed makes sure the following subscriptions are in place:
  // * buildbucket, via the settings.Buildbucket.Topic setting