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<meta charset="utf-8">
<meta name="viewport" content="width=device-width; initial-scale=1.0">
<title>Dragging the mouse on the viewport's scrollbar</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>
.content {
width: 1000px;
height: 5000px;
<script type="text/javascript">
async function test() {
let scrollPromise = new Promise(resolve => {
window.addEventListener("scroll", resolve, {once: true});
// Do the scroll in one increment so that when the scroll event fires
// we're done all the scrolling we're going to do.
var dragFinisher = await promiseVerticalScrollbarDrag(window, 20, 20);
if (!dragFinisher) {
ok(true, "No scrollbar, can't do this test");
// 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();
// After dragging the scrollbar 20px on a 1000px-high viewport, we should
// have scrolled approx 2% of the 5000px high content. There might have been
// scroll arrows and such so let's just have a minimum bound of 50px to be safe.
ok(window.scrollY > 50, "Scrollbar drag resulted in a vertical scroll position of " + window.scrollY);
// Check that we did not get spurious horizontal scrolling, as we might if the
// drag gesture is mishandled by content as a select-drag rather than a scrollbar
// drag.
is(window.scrollX, 0, "Scrollbar drag resulted in a horizontal scroll position of " + window.scrollX);
.then(subtestDone, subtestFailed);
<div class="content">Some content to ensure the root scrollframe is scrollable</div>