chromium/chrome/test/data/autofill/cross_origin_iframe.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<!-- Site including a form in a cross-origin iframe. -->
<html>
  <head>
    <title>Simple cross-site iframe</title>
  </head>
  <body>
    <iframe id="crossFrame" name="crossFrame" width=500 height=300></iframe>
  </body>
</html>