chromium/third_party/blink/web_tests/fast/forms/tabbing-input-iframe.html

<html>
<head>
    <script>
    function test() {
        document.getElementById('t1').focus();
        if (window.eventSender) {
            eventSender.keyDown("\t");
            eventSender.keyDown("\t");
        }
    }
    </script>
</head>

<body onload="test()">
    This tests that you can tab out of a text field if an iframe comes after it.<br>
    <input id="t1">
    <iframe style="border: solid thin black"></iframe>
    <input id="t2" value="This should have focus">
</body>
</html>