LayoutTests/fast/dom/Window/open-existing-pop-up-blocking.html

<script>
if (window.testRunner)
    testRunner.waitUntilDone();
</script>
<iframe src="resources/open-sibling-subframe.html"></iframe>
<iframe name="sibling" src="data:text/html,If you can still see this text, the test failed."></iframe>