chromium/chrome/test/data/page_load_metrics/sapper_page.html

<!DOCTYPE html>
<script>
  window.__SAPPER__ = {
    data: 'test'
  };
</script>
<body>
  <div>
    This is a test to see if a page with  window.__SAPPER__ is detected as
    using the Sapper JavaScript framework.
  </div>
</body>