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<!DOCTYPE HTML>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width; initial-scale=1.0">
  <title>Test for scenario in bug 1228407</title>
  <script type="application/javascript" src="apz_test_native_event_utils.js"></script>
  <script type="application/javascript" src="apz_test_utils.js"></script>
  <script src="/tests/SimpleTest/paint_listener.js"></script>
  <script type="application/javascript">

async function test() {
  let utils = SpecialPowers.getDOMWindowUtils(window);
  utils.advanceTimeAndRefresh(0);

  // Part of the problem in bug 1228407 was that the main-thread scroll
  // generation counter was continually increasing (due to scrollBy calls in
  // quick succession), and so repaint requests from APZ would get ignored (due
  // to stale scroll generation), and so the main thread scroll position would
  // never actually get updated. This loop exercises that case. The expected
  // behaviour (pre-APZ) was that the scrollBy call would actually start the
  // scroll animation and advance the scroll position a little bit, so the next
  // scrollBy call would move the animation destination a little bit, and so
  // the loop would continue advancing the scroll position. The bug resulted
  // in the scroll position not advancing at all.
  for (let i = 0; i < 100; i++) {
    document.scrollingElement.scrollBy({top:60, behavior: "smooth"});
    await promiseApzRepaintsFlushed();
    utils.advanceTimeAndRefresh(16);
  }

  utils.restoreNormalRefresh();
  await promiseApzRepaintsFlushed();

  let scrollPos = document.scrollingElement.scrollTop;
  ok(scrollPos > 60, `Scrolled ${scrollPos}px, should be more than 60`);
}

waitUntilApzStable().then(test).then(subtestDone, subtestFailed);

  </script>
  <style>
    body {
      height: 5000px;
      background: linear-gradient(red, black);
    }
  </style>
</head>
<body>
</body>
</html>