chromium/src/third_party/blink/web_tests/http/tests/priority-hints/image-element-use-counter.html

<script src=resources/common.js></script>
<script src=../resources/testharness.js></script>
<script src=../resources/testharnessreport.js></script>

<script>
  test(t => {
    t.add_cleanup(clearUseCounter);
    assert_false(internals.isUseCounted(document, kPriorityHints),
                 'Priority Hints is not use-counted before the importance ' +
                 'IDL attribute is set');
    const image = new Image();
    image.importance = 'high';
    assert_true(internals.isUseCounted(document, kPriorityHints),
                'Priority Hints is use-counted once the importance IDL ' +
                'attribute is set');
  }, 'Priority Hints use-counter works properly with the <img> importance ' +
     'IDL attribute');

  test(t => {
    t.add_cleanup(clearUseCounter);
    assert_false(internals.isUseCounted(document, kPriorityHints),
                 'Priority Hints is not use-counted before the importance ' +
                 'content attribute is set');
    const image = new Image();
    image.setAttribute('importance', 'high');
    assert_true(internals.isUseCounted(document, kPriorityHints),
                'Priority Hints is use-counted once the importance content ' +
                'attribute is set');
  }, 'Priority Hints use-counter works properly with the <img> importance ' +
     'content attribute');

  const t = async_test('Priority Hints is use-counted when the importance ' +
                       'content attribute is parsed on the <img> element');
  t.add_cleanup(clearUseCounter);

  t.step_func(() => {
    assert_false(internals.isUseCounted(document, kPriorityHints),
                 'Priority Hints is not use-counted before the importance ' +
                 'content attribute is parsed');
  });

  window.addEventListener('DOMContentLoaded', t.step_func_done(() => {

    document.body.innerHTML +=
                            '<img importance=high src../resources/square.png>';
    assert_true(internals.isUseCounted(document, kPriorityHints),
                'Priority Hints is use-counted once the importance content ' +
                'attribute is parsed');
  }));
</script>