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chromium/third_party/blink/web_tests/http/tests/security/resources/cross-frame-iframe-for-object-getPrototypeOf-test.html 

<html>
<head>
    <script>
        onload = function()
        {
            parent.postMessage("finishedLoad", "*");
        }
    </script>
</head>
<body>
    Body
</body>
</html>