 => {
    assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.');
    window.addEventListener('message', t.step_func(e => {
      assert_equals(e.data['entryType'], 'longtask');
      assert_equals(e.data['frame-attribution'], 'cross-origin-unreachable');
      assert_equals(e.data['task-attribution'], 'unknown');
      assert_equals(e.data['containerType'], 'window');
      assert_equals(e.data['containerId'], '');
      assert_equals(e.data['containerName'], '');
      assert_