chromium/third_party/blink/web_tests/editing/selection/focus-contenteditable-iframe.html

<html>
<body>
<script src="../../resources/dump-as-markup.js"></script>
<script>
Markup.description("This tests focusing the body element in a contentEditable iframe. The whole body contents should be selected. Focus should only place the cursor at the beginning of the body if there isn't an existing selection.");

function handleLoad() {
    var win = document.querySelector('iframe').contentWindow;
    var body = win.document.body;
    body.innerHTML = "asdf";
    body.contentEditable = true;
    win.getSelection().selectAllChildren(body);
    body.focus();
    Markup.dump(win.document);
};
</script>
<iframe onload="handleLoad()"></iframe>

</body>
</html>