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

<!-- A page that is used to test that a dynamic form fill feature works properly. -->
<body>
  <form name="addr1.1" id="form1" action="https://example.com/" method="post">
    Name: <input type="text" name="firstname" id="firstname" autocomplete="given-name"><br>
    Address: <input type="text" name="address1" id="address1"><br>
    City: <input type="text" name="city" id="city"><br>
    State/Province:
    <select name="state_ca" id="state_ca" autocomplete="region">
      <option value="BC">BC</option>
      <option value="QC">QC</option>
      <option value="NS">NS</option>
      <option value="AL">AL</option>
      <option value="ON">ON</option>
    </select> <br>
    <input type="text" name="state_us" id="state_us" style="display: none;" autocomplete="region"><br>
    Zip: <input name="zip" id="zip"> <br>
    Country: <select name="country" id="country" onchange="CountryChanged()">
      <option value="CA">Canada</option>
      <option value="US">United States</option>
    </select> <br>
    Company: <input name="company" id="company"> <br>
    Email: <input name="email" id="email"> <br>
    Phone: <input name="phone" id="phone"> <br>
    <input type="reset" value="Reset">
    <input type="submit" value="Submit" id="profile_submit">
  </form>
</body>

<script>
function CountryChanged() {
  var first_name_input = document.getElementById("firstname");
  // Reset the value of the first name field.
  first_name_input.value = '';

  // Get the select object for states of canada and hide it.
  var state_ca = document.getElementById("state_ca");
  state_ca.setAttribute('style', "display: none;");
  var state_us = document.getElementById("state_us");
  state_us.removeAttribute('style');

  window['refill'] = true;
  console.log('An event happened that should trigger a refill.');
}
</script>