Function buildErrorMessage_

src/error-reporting.js:463–477

* @param {string|undefined} message * @param {*|undefined} error * @return {string}

(message, error)

 * @return {string}
 */
function buildErrorMessage_(message, error) {
  if (error) {
    if (error.message) {
      message = error.message;
    } else {
      // This should never be a string, but sometimes it is.
      message = String(error);
    }
  }
  if (!message) {
    message = 'Unknown error';
  }

  return message;
}

/**
 * Signature designed, so it can work with window.onerror