<!DOCTYPE html>
<script>
var channel = new MessageChannel();
channel.port1.start();
channel.port1.close();
window.top.postMessage('gcMe', '*');
</script>
<!DOCTYPE html>
<script>
var channel = new MessageChannel();
channel.port1.start();
channel.port1.close();
window.top.postMessage('gcMe', '*');
</script>