third_party/blink/manual_tests/animation/compositor-animation-direction.html

<html>
<style>
div {
    position: relative;
    height: 100px;
    width: 100px;
    background: blue;
    transform: translateZ(0);
    animation-duration: 2s;
    animation-timing-function: linear;
    animation-fill-mode: both;
    animation-iteration-count: 2;
}

.normal {
    animation-direction: normal;
}

.reverse {
     animation-direction: reverse;
}

.alternate {
     animation-direction: alternate;
}

.alternate-reverse {
     animation-direction: alternate-reverse;
}

.anim-left {
    animation-name: anim-left;
    z-index: 100;
}

.anim-transform {
    animation-name: anim-transform;
    z-index: 200;
}

@keyframes anim-left {
    0% {
        left: 0px;
    }
    100% {
        left: 300px;
    }
}

@keyframes anim-transform {
    0% {
        transform: translateX(0px);
    }
    100% {
        transform: translateX(300px);
    }
}
</style>
<body>
<p>
Each section below has two boxes, the top runs on the main thread, the bottom
on the compositor. The animations should be identical but start at different
times.
</p><p>
This test is successful if the each pair of boxes are mostly in sync (there
might be a small offset between them).
</p>
<hr>

Direction normal - forwards twice
<br>
<div class='normal anim-left'></div>
<div class='normal anim-transform'></div>

Direction reverse - backwards twice
<br>
<div class='reverse anim-left'></div>
<div class='reverse anim-transform'></div>

Direction alternate - forwards then backwards
<br>
<div class='alternate anim-left'></div>
<div class='alternate anim-transform'></div>

Direction alternate-reverse - backwards then forwards
<br>
<div class='alternate-reverse anim-left'></div>
<div class='alternate-reverse anim-transform'></div>

</body>
</html>