chromium/third_party/blink/web_tests/http/tests/loading/simple-subframe.html

<script>
if (window.testRunner)
  testRunner.dumpAsText();
</script>
This is a test of load callbacks. It is only useful inside the regression test tool.<br>
<iframe name="f1" src="data:text/html,<b>test</b>"></iframe>