 {
    assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
    const img_src = '/element-timing/resources/progressive-image.py?name=square20.jpg&numInitial='
      + numInitial + '&sleep=' + sleep;
    const img1 = document.getElementById('target')
    img1.src = img_src;
    // After a brief wait, remove the image and add a smaller image to target2.
    t.step_timeout(() => {
      img1.parentNode.removeChild(img1);
      document.getElementById('target2').src = s