chromium/third_party/blink/web_tests/http/tests/messaging/resources/cross-domain-message-receive.html

<!DOCTYPE html>

<html lang="en">
<head>
    <title>Cross-Doc Test</title>
</head>
<script type="text/javascript" charset="utf-8">

function receiver(e) {
    var result = "";
    result += "data: " + e.data + "\n";
    result += "origin: " + e.origin + "\n";
    e.source.postMessage(result, "*");   
}

addEventListener('message', receiver, false);

</script>
<body>
    
</body>
</html>