chromium/chrome/test/data/banners/fenced_frames/manifest_test_page.html

<html>
  <head>
    <title>Web app banner test page</title>
    <script src="/banners/main.js"></script>
    <script>
      // If a "manifest=/path/to/manifest.json" query argument is provided to
      // the URL accessing this page, that path is injected as the manifest tag.
      // Otherwise, "manifest.json" is used as the manifest tag.
      addManifestLinkTag();
    </script>
  </head>
  <body onload="initializeWithWorker('/banners/service_worker.js')">
    Service worker returns a response object if it's offline, so the page
    supports the offline environment.
  </body>
</html>