etc/ci/performance/page_load_test/example/example_async.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width" />
    <title></title>
  </head>
  <body>
  Hello World
  <!-- Remember to include the /harness/harness.js file
       for the mark() and done() function -->
  <script src="/harness/harness.js" type="text/javascript" charset="utf-8"></script>
  <script type="text/javascript" charset="utf-8">
    // Create a timestamp before the test
    mark("test start");
    // Do something slow here
    // Create another timestamp after the test
    mark("test end");
    // Tell the test harness you're done, otherwise it will keep waiting
    done();
  </script>
  </body>
</html>