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chromium/third_party/blink/web_tests/fast/forms/select/listbox-overlay-scrollbar.html 

<!DOCTYPE html>
<html>
<head>
<script>
if (window.internals)
  internals.useMockOverlayScrollbars();
</script>
<style>
html, body {
    margin: 0;
    padding: 0;
}
.sel {
    border: 0;
    width: 100px;
    height: 100px;
    background-color: lime;
    display: block;
    font-family: "Arial";
    font-size : 12pt;
}
</style>
</head>
<body>
<p>You should see 2 green boxes with overlay scrollbar. The second box
should have a scrollbar on the left.</p>

<div>
<select multiple class="sel" size="5">
<option>foo1</option>
<option>foo2</option>
<option>foo3</option>
<option>foo4</option>
<option>foo5</option>
</select>
</div>
<div>
<select multiple dir="rtl" class="sel" size="5">
<option>foo1</option>
<option>foo2</option>
<option>foo3</option>
<option>foo4</option>
<option>foo5</option>
</select>
</div>
</body>
</html>