<!DOCTYPE html>

<html>
<head>
    <style>
        .container {
            position: relative;
            height: 200px;
            width: 500px;
            border: 1px solid black;
            overflow: hidden;
            z-index: 0;
        }
        
        .box {
            position: absolute;
            left: -100px;
            width: 200px;
            height: 200px;
            background-color: blue;
            -webkit-animation: move 20000000s linear;
        }
        
        @-webkit-keyframes move {
            from { -webkit-transform: none; }
            to   { -webkit-transform: translateX(400px); }
        }
    </style>
    <script>
        if (window.testRunner) {
            testRunner.dumpAsText();
            testRunner.waitUntilDone();
        }

        function doTest()
        {
            const animated = document.getElementById('animated');
            animated.classList.add('animating');
            animated.getAnimations()[0].ready.then(() => {
                if (window.internals)
                    document.getElementById('layers').innerText = internals.layerTreeAsText(document, internals.LAYER_TREE_INCLUDES_VISIBLE_RECTS)

                if (window.testRunner)
                    testRunner.notifyDone();
            });
        }
        window.addEventListener('load', doTest, false);
    </script>
</head>
<body>

    <div class="container">
        <div id="animated" class="box"></div>
    </div>

<pre id="layers">Layer tree goes here when testing</pre>
</body>
</html>