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chromium/chrome/test/data/extensions/api_test/identity/redirect_after_load.html 

<html>
<head><title>OK</title></head>
<body>
  <script>
    window.addEventListener('load', () => {
      setTimeout(redirect, 10);
    });

    const redirect = () => {
      window.location.href = 'https://abcdefghij.chromiumapp.org/callback#test';
    };
  </script>
</body>
</html>