chromium/third_party/blink/web_tests/external/wpt/requestidlecallback/callback-iframe.html

<!doctype html>
<meta charset=utf-8>
<title></title>
<meta name="timeout" content="long">
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<div id="log"></div>
<iframe style="display:none" id="frame"></iframe>
<script>
  async_test(function (t) {
    let frame = document.getElementById("frame");
    frame.contentWindow.test = function() {
      frame.contentWindow.requestIdleCallback(t.step_func_done());
    }

    frame.contentWindow.test();
  });
</script>