chromium/third_party/blink/web_tests/fast/events/resources/frame-tab-focus-upper.html

<html>
<style>
body {
background-color: white;
}

iframe {
border: 2px solid black;
}
</style>
<script>
window.parent.setupWindow(window);
</script>
<body onload="window.setupBody();">
<iframe id="middle" src="frame-tab-focus-middle.html" width="500" height="200"></iframe>
</body>
</html>