chromium/chrome/test/data/password/password_form_in_credentialless_iframe.html

<html>
<body>
<script>
  function create_iframe(src, id, anonymous) {
    return new Promise(resolve => {
      let iframe = document.createElement("iframe");
      iframe.credentialless = anonymous;
      iframe.id = id;
      iframe.src = src;
      document.body.appendChild(iframe);
      iframe.onload = resolve;
    });
  }

  async function check_password(child) {
    const element = child.getElementById('password');
    return new Promise(async resolve => {
      element.onchange = () => {
        if (element.value) {
          resolve(element.value);
        }
      };
      element.onchange();
      setTimeout(() => resolve("not found"), 1000);
    });
  }

  function inject_form(child) {
    let form = child.createElement('form');
    form.method = "POST";
    form.name = "TestForm";
    form.action = "/password/done.html";
    child.body.appendChild(form);
    let username = child.createElement('input');
    username.id = "username";
    username.type = "text";
    username.autocomplete = "username";
    form.appendChild(username);
    let input = child.createElement('input');
    input.id = "password";
    input.type = "password";
    input.autocomplete = "password";
    form.appendChild(input);
  }
</script>

</body>
</html>