code: func newDownloader(client *http.Client) (*downloader, error) {
  	srv, err := drive.New(client)
  	if err != nil {
  		return nil, err
  	}
  	return &downloader{
  		rate:    rate.NewLimiter(defaultRateLimit, 1),
  		Service: srv,
  	}, nil
  }
docs: // newDownloader returns a downloader with the given http.Client
  // to download photos.
  //
  // The client must be authenticated for drive.DrivePhotosReadonlyScope
  // ("https://www.googleapis.com/auth/drive.photos.readonly")..