chromium/third_party/blink/web_tests/wpt_internal/shadow-dom/shadow-dom-usecounter.html

<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<body>
<div id="container"></div>
<div id="placeholder" role="searchbox"></div>
<input id="input-container"></input>

<script type="module">
import {WebFeature} from '/gen/third_party/blink/public/mojom/use_counter/metrics/web_feature.mojom.m.js';

test(() => {
  // Verify that aria-placeholder is counted in light DOM.
  internals.clearUseCounter(document, WebFeature.kARIAPlaceholderAttribute);
  var domPlaceholder = document.getElementById('placeholder');
  domPlaceholder.setAttribute('aria-placeholder', 'MM-DD-YYYY');
  assert_true(internals.isUseCounted(document, WebFeature.kARIAPlaceholderAttribute));

  // <input type=datetime-local> generates shadow DOM and makes use of the aria-placeholder attribute.
  internals.clearUseCounter(document, WebFeature.kARIAPlaceholderAttribute);
  assert_false(internals.isUseCounted(document, WebFeature.kARIAPlaceholderAttribute), "Check that the attribute has been cleared.");
  var input = document.getElementById('input-container');
  input.setAttribute('type', 'datetime-local');
  assert_not_equals(internals.shadowRoot(input).querySelector('[aria-placeholder]'), null, "Attribute should exist in UA shadow DOM");
  assert_false(internals.isUseCounted(document, WebFeature.kARIAPlaceholderAttribute), "Attribute should not be counted in UA shadow DOM.");
}, "Attributes should not be counted in user agent shadow DOM.");
</script>
</body>