code: func (s *Service) BackfillTagIndex(tagKey string) *BackfillTagIndexCall {
  	c := &BackfillTagIndexCall{s: s, urlParams_: make(gensupport.URLParams)}
  	c.urlParams_.Set("tag_key", tagKey)
  	return c
  }
docs: // BackfillTagIndex: Backfills TagIndex entites from builds.