code: func GitilesBuildSet(c *pb.GitilesCommit) string {
  	return fmt.Sprintf("commit/gitiles/%s/%s/+/%s", c.Host, c.Project, c.Id)
  }
docs: // GitilesBuildSet returns a buildset representation of c.
  // e.g. "commit/gitiles/chromium.googlesource.com/infra/luci/luci-go/+/b7a757f457487cd5cfe2dae83f65c5bc10e288b7"