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

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

<script>clearUseCounter()</script>
<img id="img" src="../resources/dummy.png" importance="low">

<script>
  const t = async_test('Priority Hints is use-counted when the importance ' +
                       'content attribute is parsed on <img>s that are ' +
                       'fetched by the preload scanner');

  window.onload = t.step_func_done(() => {
    assert_true(internals.isPreloaded(img.src),
                'The <img> resource was ' + 'fetched by the preload scanner');
    assert_true(internals.isUseCounted(document, kPriorityHints),
                'Priority Hints is use-counted when the preload scanner ' +
                'fetches an <img> with an importance attribute');
  });
</script>