chromium/chrome/test/data/optimization_guide/hello.html

<!DOCTYPE html>
<html>
<head>
  <title>Test Page</title>

  <!-- This script is provided by the browsertest, but is intentionally slow.
    This provides important time between commit and first layout for any text
    dump requests to make it to the renderer, reducing flakes. -->
  <script type="text/javascript" src="/slow-first-layout.js"></script>
</head>
<body>
  <p>hello</p>
</body>
</html>