chromium/third_party/blink/web_tests/media/controls/lazy-loaded-style.html

<!DOCTYPE html>
<html>
<script src="../media-controls.js"></script>
<title>Test that media controls are styled correctly if lazy loaded.</title>
<video width="400"></video>
<script>
  var video = document.querySelector('video');
  enableTestMode(video);

  if (window.testRunner)
    testRunner.waitUntilDone();

  video.addEventListener('loadeddata', () => {
    video.controls = true;

    if (window.testRunner)
      testRunner.notifyDone();
  }, { once: true });

  video.src = "../content/test.ogv";
  video.load();
</script>
</html>