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Test Info:

<!DOCTYPE HTML>
<html>
<!--
-->
<head>
<meta charset="utf-8">
<title>Test for Bug 1247074</title>
<script src="/tests/SimpleTest/SimpleTest.js"></script>
<script src="/tests/SimpleTest/paint_listener.js"></script>
<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
<style>
.outer {
direction: ltr;
height: 400px;
width: 415px;
overflow: hidden;
position: relative;
}
.inner {
height: 100%;
outline: none;
overflow-x: hidden;
overflow-y: scroll;
position: relative;
scroll-behavior: smooth;
}
.outer.contentBefore::before {
top: 0;
content: '';
display: block;
height: 2px;
position: absolute;
width: 100%;
z-index: 99;
}
</style>
</head>
<body>
<p id="display"></p>
<div class="outer">
<div class="inner">
<ol>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
<li>Some text</li>
</ol>
</div>
</div>
<script>
SimpleTest.waitForExplicitFinish();
window.onload = function() {
var elm = document.getElementsByClassName('inner')[0];
// Take control of the refresh driver
var utils = SpecialPowers.DOMWindowUtils;
utils.advanceTimeAndRefresh(0);
// Start a smooth scroll and advance a couple of frames so we're in the
// middle of the scroll animation
elm.scrollTop = 500;
utils.advanceTimeAndRefresh(16);
utils.advanceTimeAndRefresh(16);
// Trigger a frame reconstruction
elm.parentNode.classList.add('contentBefore');
// Reach a stable state and verify the scroll position is 500
utils.restoreNormalRefresh();
waitForAllPaintsFlushed(function() {
SimpleTest.is(elm.scrollTop, 500, "Scroll position ended up at 500");
SimpleTest.finish();
});
}
</script>
</body>
</html>