chromium/chrome/test/data/background_fetch/background_fetch.html

<!doctype html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>BackgroundFetchBrowserTest helper page</title>
    <script src="../format_error.js"></script>
    <script src="background_fetch.js"></script>
  </head>
  <body>
    <!-- Logic located in background_fetch.js. -->
  </body>
</html>