chromium/src/third_party/blink/web_tests/fast/frames/srcdoc/setting-srcdoc-reloads-document.html

<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.waitUntilDone();
}

function pass() {
    document.getElementById('result').textContent = 'PASS';
    if (window.testRunner)
        testRunner.notifyDone();
}
</script>
<p>This test ensures that setting the srcdoc attribute iframe causes the
document to change to the current value of the srcdoc attribute on the
iframe.</p>
<div id="result">Waiting...</div>
<iframe srcdoc="
  <script>
  window.frameElement.srcdoc = '<script>top.pass();<\/script>';
  </script>
"></iframe>