static normalizeUrl(url) {
    // Verify the url is valid and that protocol is allowed
    if (url && this.isValid(url) && this.isProtocolAllowed(url)) {
      // Use canonicalized URL (with trailing slashes and such)
      return new URL(url).href;
    } else {
      throw new LighthouseError(LighthouseError.errors.INVALID_URL);
    }
  }
@param {string|undefined} url
@return {string}