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chromium/fuchsia_web/webengine/test/data/visibility.html 

<!DOCTYPE html>
<!--
Copyright 2020 The Chromium Authors
Use of this source code is governed by a BSD-style license that can be
found in the LICENSE file.
-->
<html>
  <head><title>unset</title></head>
  <body>
    <script>
        document.title = document.visibilityState;
        document.addEventListener('visibilitychange', function(e) {
          document.title = document.visibilityState;
        });
    </script>
  </body>
</html>