<!DOCTYPE html>

<html>
<head>
    <style>
        body {
            height: 1200px;
        }
        .box {
          width: 100px;
          height: 100px;
          margin: 50px;
          background-color: blue;
          border: 2px solid black;
        }
        
        #box {
            background-image: linear-gradient(to top, white, black);
            background-attachment: fixed;
            background-repeat: no-repeat;
        }
        
        #box.hidden {
            display: none;
        }

        #box.loaded {
            background: transparent;
        }
    </style>
    <script>
        if (window.testRunner)
            testRunner.dumpAsText();

        function doTest()
        {
            var box = document.getElementById('box');
            box.classList.add('hidden');
            document.body.offsetWidth;
            box.classList.remove('hidden');
            document.body.offsetWidth;
            box.classList.add('loaded');
            
            if (window.internals)
                document.getElementById('reasons').textContent = window.internals.synchronousScrollingReasons();
        }
        window.addEventListener('load', doTest, false);
    </script>
</head>
<body>

    <div id="box" class="box"></div>
    <p>Test passes if there are no reasons for slow scrolling below.</p>
<pre id="reasons"></pre>
</body>
</html>