frame-reconstruction-scroll-clamping.html

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<html class="reftest-wait">

<!--

For bug 1266833; syncing the scroll offset to APZ properly when the scroll

position is clamped to a smaller value during a frame reconstruction.

-->

<script>

    function run() {

        document.body.scrollTop = document.body.scrollTopMax;

        // Let the scroll position propagate to APZ before we do the frame

        // reconstruction. Ideally we would wait for flushApzRepaints here but

        // we don't have access to DOMWindowUtils in a reftest, so we just wait

        // 100ms to approximate it. With bug 1266833 fixed, this test should

        // never fail regardless of what this timeout value is.

        setTimeout(frameReconstruction, 100);

    function frameReconstruction() {

        document.body.classList.toggle('noscroll');

        document.documentElement.classList.toggle('reconstruct-body');

        document.getElementById('spacer').style.height = '100%';

        document.documentElement.classList.remove('reftest-wait');

</script>

<style>

    html, body {

        margin: 0;

        padding: 0;

        background-color: green;

    .noscroll {

        overflow: hidden;

        height: 100%;

    /* Toggling this on and off triggers a frame reconstruction on the <body> */

    html.reconstruct-body::before {

        top: 0;

        content: '';

        display: block;

        height: 2px;

        position: absolute;

        width: 100%;

        z-index: 99;

</style>

<body onload="setTimeout(run, 0)">

 <div id="spacer" style="height: 5000px">

  This is the top of the page.

 </div>

 This is the bottom of the page.

</body>