<html>
<head>
<script>
var doMutation = function() {
  var region = document.getElementById("to_mutate");
  var to_remove = document.getElementById("to_remove");
  region.removeChild(to_remove);
  window.setTimeout(function() { window.close(); } );
}
window.addEventListener("load", doMutation);
</script>
</head>
<body>
<div id="to_mutate" aria-live="polite" aria-relevant="removals" aria-atomic="false">
  Some contents
  <div id="to_remove">
    Contents to be removed
  </div>
</div>
</body>
</html>