LayoutTests/fast/overflow/scrollbar-position-update.html

<p>
    Test for <i><a href="http://bugs.webkit.org/show_bug.cgi?id=16426">http://bugs.webkit.org/show_bug.cgi?id=16426</a>
    Divs with overflow:auto: scrollbars not correctly updated when contents change</i>.
</p>
<p>
    The thumb should be in the middle of the scroll bar.
</p>
<div id="outer" style="height: 200px; width: 200px; overflow-y: scroll;">
    <div id="inner" style="height: 400px;">
    </div>
</div>
<script>
    document.getElementById("outer").scrollTop = 200;
    document.getElementById("inner").style.height = "600px";
</script>