chromium/third_party/blink/web_tests/external/wpt/html/semantics/document-metadata/the-style-element/style_load_async.html

<!doctype html>
<html>
<meta charset="utf-8">
<title>Style load event should be async</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
    var t = async_test("style load should be async");
    var sync = true;
    function check() {
        assert_false(sync);
        t.done();
    }
</script>
<style onload="t.step(check)">
</style>
<script>
  sync = false
</script>

<body>
  <div id="log"></div>
  <div id="test"></div>
</body>
</html>