);
  // Wait for the initial render to complete.
  await waitForAnimationFrames(2);

  const startTime = performance.now();
  return new Promise(resolve => {
    new PerformanceObserver(t.step_func(list => {
      const endTime = performance.now();
      assert_equals(list.getEntries().length, 1);
      const entry = list.getEntries()[0];
      assert_equals(entry.entryType, "layout-shift");
      assert_equals(entry.name, "");
      assert_greater_than_equal(entry.startTime, startTime);
      assert_less_t