chromium/chrome/test/data/extensions/api_test/app_process/path3/iframe.html

<script>
  // Open popup to another normal web page, same-origin and non-app.
  window.open(
      '/extensions/api_test/app_process/path3/empty.html',
      '',
      // Small enough that a popup will be created even on Chrome OS
      'width=200,height=200');
</script>