third_party/WebKit/Source/web/tests/data/fixed-position-losing-backing.html

<!DOCTYPE html>
<style>
#fixed {
    position: fixed;
    width: 100px;
    height: 100px;
    /* Using transparent background color so that fixed position element is not automatically promoted. */
    background-color: rgba(255, 255, 0, 0.5);
    transform: translateZ(0);
}

#bloat {
    height: 10000px;
}
</style>
<div id="fixed"></div>
<div id="bloat"></div>