code: function getErrorReportURL(projectId, key) {
    var url = [API, projectId, 'events:report'].join('/');
    if (isString(key)) {
      url += '?key=' + key;
    }
    return url;
  }
docs: Compute the URL that errors should be reported to given the projectId and
  optional key.
  @param {String} projectId - the project id of the application.
  @param {String|Null} [key] - the API key used to authenticate against the
  service in place of application default credentials.
  @returns {String} computed URL that the errors should be reported to.
  @private