<html>
<style>
body {
    height: 5000px;
    width: 5000px;
}
</style>
<script>
window.onload = function () {
    if (window.testRunner && window.internals) {
        testRunner.dumpAsText(true);
        internals.installMockPageOverlay("document");
        internals.installMockPageOverlay("view");

        var layersResult = document.getElementById('layers');
        layersResult.innerText = window.internals.pageOverlayLayerTreeAsText();
    }
}
</script>
<body>
    <pre id="layers" style="position: absolute; height: 1px; width: 1px; overflow: hidden;"></pre>
</body>
</html>