<!DOCTYPE html>
<html>
<style>
    body { margin: 0; }

    #button {
        display: inline-block;
        width: 100px;
        height: 100px;
        background-color: green;
        cursor: pointer;
        border-radius: 10px;
    }
</style>
<body>
<div id="button" onclick="2+2"></div>

<pre id="results"></pre>
<script>
if (window.testRunner)
    testRunner.dumpAsText();

window.onload = function () {
    document.getElementById("button").onclick = null;

    if (window.internals)
       results.textContent = internals.layerTreeAsText(document, internals.LAYER_TREE_INCLUDES_EVENT_REGION | internals.LAYER_TREE_INCLUDES_ROOT_LAYER_PROPERTIES);
};
</script>
</body>
</html>