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chromium/third_party/blink/web_tests/paint/invalidation/scroll/overflow-scroll-body-appear.html 

<!DOCTYPE html>
<html>
<head>
    <script src="../resources/text-based-repaint.js" type="text/javascript"></script>
    <script>
        function repaintTest()
        {
            document.body.style.overflow = "visible";
        }
    </script>
</head>

<body style="overflow:hidden" onload="runRepaintAndPixelTest()">
    <p>You should see both vertical and horizontal scrollbars.
    <p>This is the test for <a href="https://bugs.webkit.org/show_bug.cgi?id=36461">Bug 36461 - No vertical scrollbar after the CSS class change</a>.

    <div style="width: 2000px; height: 2000px;">
</body>
</html>