chromium/third_party/blink/web_tests/compositing/iframes/resources/fixed-position-subframe.html

<html>
<head>
<script src="../../../resources/run-after-layout-and-paint.js"></script>
<style>
    body {
        height: 5000px;
        background-color: red;
        overflow: hidden;
    }

    #trigger {
        will-change:transform;
    }

    #overlap {
        width: 1000px;
        height: 1000px;
        background-color: green;
        position: fixed;
        left: 0px;
        top: 0px;
    }
</style>
</head>
<script>
    function doTest() {
        window.scrollTo(0, 2000);
        runAfterLayoutAndPaint(function() {
            window.scrollTo(0, 1800);
        }, true);
    }
    window.addEventListener("load", doTest, false);
</script>
<body>
    <div id="trigger"></div>
    <div id="overlap"></div>
</body>
</html>