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chromium/third_party/blink/web_tests/http/tests/security/aboutBlank/resources/iframe-with-about-blank-children.html 

<html>
<head>
<script>
document.cookie = 'cookie=resources';
</script>
</head>
<body>
<iframe src="about:blank"></iframe>
<iframe src=""></iframe>
</body>
</html>