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chromium/third_party/blink/web_tests/fast/frames/srcdoc/srcdoc-beats-src-dom.html 

<body>
<script>
if (window.testRunner)
    testRunner.dumpAsText();

var ifrm = document.createElement("iframe");
ifrm.srcdoc = "PASS";
ifrm.src = "data:text/html,<script>alert(/FAIL/);<\/script>";
document.body.appendChild(ifrm);
</script>
This test passes if it doesn't alert FAIL.