getReadableError_() {
    switch (this.type) {
      case ModuleLoadFailure.Type.UNAUTHORIZED:
        return 'Unauthorized';
      case ModuleLoadFailure.Type.CONSECUTIVE_FAILURES:
        return 'Consecutive load failures';
      case ModuleLoadFailure.Type.TIMEOUT:
        return 'Timed out';
      case ModuleLoadFailure.Type.OLD_CODE_GONE:
        return 'Out of date module id';
      case ModuleLoadFailure.Type.INIT_ERROR:
        return 'Init error';
      default:
        return `Unknown failure type ${this.type}`;
    }
  }
Gets a human readable error message for a failure type.
@return {string} The readable error message.
@private