code: func validateFaviconURL(faviconURL string) error {
  	parsedFaviconURL, err := url.Parse(faviconURL)
  	if err != nil {
  		return err
  	}
  	host := strings.SplitN(parsedFaviconURL.Host, ":", 2)[0]
  	if host != "storage.googleapis.com" {
  		return fmt.Errorf("%q is not a valid FaviconURL hostname", host)
  	}
  	return nil
  }
docs: // validateFaviconURL checks to see if the URL is well-formed and the host is in
  // the whitelist.