    new Container('object', 'data'),
    new Container('embed', 'src'),
];
Containers.forEach(container => {
  promise_test(async t => {
    assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.');
    const initialTime = performance.now();
    const performanceObserverTimeout = 5 * 1000;
    const testLongTaskEntry = new Promise(resolve => {
      const observer = new PerformanceObserver(t.step_func(entryList => {
        const entries = entryList.getEntries();
        entries.f