chromium/third_party/blink/renderer/core/testing/data/find_in_generated_frame.html

<!DOCTYPE html>
<html>
<head>
<script>
  function createFrame() {
    var generatedFrame = document.createElement('iframe');
    generatedFrame.setAttribute("srcdoc", "<b>Foo</b>");
    document.body.appendChild(generatedFrame);
  }

  window.onload = createFrame;
</script>
</head>
<body>
test
</body>
</html>