code: func NewProdClient(ctx context.Context, rt http.RoundTripper) (Client, error) {
  	c := prodClient{
  		Context: ctx,
  		rt:      rt,
  	}
  	var err error
  	c.baseClient, err = c.newClient()
  	if err != nil {
  		return nil, err
  	}
  	return &c, nil
  }
docs: // NewProdClient creates a new Client instance that uses production Cloud
  // Storage.
  //
  // The supplied RoundTripper will be used to make connections. If nil, the
  // default HTTP client will be used.