<!DOCTYPE html>

<html>
<head>
    <style>
        .container {
            height: 300px;
            width: 400px;
            border: 2px solid black;
            overflow: hidden;
        }

        .box {
            height: 300px;
            width: 2800px;
            border: 1px solid black;
            background-color: gray;
        }

        .composited {
            transform: translateZ(0);
        }

        .masked {
            -webkit-mask-image: url(../resources/alpha-gradient.png);
            -webkit-mask-repeat: repeat-x;
        }
    </style>
    <script>
        if (window.testRunner) {
            testRunner.dumpAsText();
            testRunner.waitUntilDone();
        }
        
        function getUIScript()
        {
            return `
            (function() {
                uiController.removeViewFromWindow(function() {
                    uiController.uiScriptComplete('');
                });
            })();`
        }

        function dumpTiles(outputId)
        {
            if (window.internals)
                document.getElementById(outputId).innerText = internals.layerTreeAsText(document, internals.LAYER_TREE_INCLUDES_TILE_CACHES);
        }
        function doTest()
        {
            if (!testRunner.runUIScript)
                return;

            dumpTiles('before-layers');

            testRunner.runUIScript(getUIScript(), function(result) {
                dumpTiles('after-layers');
                if (window.testRunner)
                    testRunner.notifyDone();
            });
        }
        window.addEventListener('load', doTest, false);
    </script>
</head>
<body>
    <div class="composited container">
        <div class="composited masked box"></div> 
    </div>

<pre id="before-layers">Layer tree goes here</pre>
<pre id="after-layers">Layer tree goes here</pre>
</body>
</html>