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<!DOCTYPE HTML>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width; initial-scale=1.0">
  <title>Dragging the mouse on a scrollbar for a scrollframe inside nested transforms</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="text/javascript">

async function test() {
  var scrollableDiv = document.getElementById("scrollable");
  let scrollPromise = new Promise(resolve => {
    scrollableDiv.addEventListener("scroll", resolve, {once: true});
  });

  // Scroll down a small amount (10px). The bug in this case is that the
  // scrollthumb "jumps" by an additional 40 pixels (height of the "gap" div)
  // and the scrollframe scrolls by a corresponding amount. So after doing this
  // drag we check the scroll position to make sure it hasn't scrolled by
  // too much.
  // Given the scrollable height of 2000px and scrollframe height of 400px,
  // the scrollthumb should be approximately 80px tall, and dragging it 10px
  // should scroll approximately 50 pixels. If the bug manifests, it will get
  // dragged 50px and scroll approximately 250px.
  var dragFinisher = await promiseVerticalScrollbarDrag(scrollableDiv, 10, 10);
  if (!dragFinisher) {
    ok(true, "No scrollbar, can't do this test");
    return;
  }

  // the events above might be stuck in APZ input queue for a bit until the
  // layer is activated, so we wait here until the scroll event listener is
  // triggered.
  await scrollPromise;

  await dragFinisher();

  // Flush everything just to be safe
  await promiseOnlyApzControllerFlushed();

  // In this case we just want to make sure the scroll position moved from 0
  // which indicates the thumb dragging worked properly.
  ok(scrollableDiv.scrollTop < 100, "Scrollbar drag resulted in a scroll position of " + scrollableDiv.scrollTop);
}

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

  </script>
</head>
<body>
    <div id="gap" style="min-height: 40px"></div>
    <div style="height: 400px; transform: translateZ(0)">
        <div style="height: 100%; opacity: 0.9; will-change: opacity">
            <div id="scrollable" style="height: 100%; overflow-y: auto; transform: translateZ(0)">
                <div style="min-height: 2000px">Yay text</div>
            </div>
        </div>
    </div>
</body>
</html>