chromium/third_party/blink/web_tests/external/wpt/focus/support/focus-already-focused-iframe-middle.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>Middle</title>
<script>
window.onmessage = function(e) {
    parent.postMessage(e.data, "*");
}
</script>
</head>
<body>
<iframe src="focus-already-focused-iframe-inner.html"></iframe>
</body>
</html>