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chromium/third_party/blink/web_tests/http/tests/misc/resources/submit-in-sibling-frame.html 

<body>
<form action="success-notify-parent.html" id="theform" method="post" name="theform" target="formframe"></form>
<script>
document.forms['theform'].submit();
location.href = "success-notify-parent.html";
</script>