about-blank-replacement-blank-dynamic-nested-frame.html

<!doctype html>
<html>
<body>
<script>
function nestedLoaded() {
  parent.postMessage({ type: 'NESTED_LOADED' }, '*');
}

// dynamically add an about:blank iframe
var f = document.createElement('iframe');
f.onload = nestedLoaded;
document.body.appendChild(f);

// Helper routine to make it slightly easier for our parent to find
// the nested frame.
function nested() {
  return f.contentWindow;
}
</script>
</body>
</html>

chromium/third_party/blink/web_tests/external/wpt/service-workers/service-worker/resources/about-blank-replacement-blank-dynamic-nested-frame.html