Web Animations: Compositor timeOffset should not be scaled

ManualTests/animation/compositor-change-playback-rate.html

Index: ManualTests/animation/compositor-change-playback-rate.html
diff --git a/ManualTests/animation/compositor-change-playback-rate.html b/ManualTests/animation/compositor-change-playback-rate.html
new file mode 100644
index 0000000000000000000000000000000000000000..712c452a0e991893b28bb1f4b8268b9993ecc7c2
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+++ b/ManualTests/animation/compositor-change-playback-rate.html
@@ -0,0 +1,42 @@
+<style>
+div {
+  height: 100px;
+  width: 100px;
+  background: blue;
+}
+</style>
+<p>
+The four squares should make identical rotations at different rates without jumping.
+<div id="target1"></div>
+<div id="target2"></div>
+<div id="target3"></div>
+<div id="target4"></div>
+<script>
+var player1 = target1.animate([
+  {transform: 'none'},
+  {transform: 'rotate(90deg)'}
+], {duration: 1000, iterations: 200000});
+
+var player2 = target2.animate([
+  {transform: 'none', background: 'blue'},
+  {transform: 'rotate(90deg)', background: 'blue'}
+], {duration: 1000, iterations: 200000});
+
+var player3 = target3.animate([
+  {transform: 'none'},
+  {transform: 'rotate(90deg)'}
+], {duration: 1000, iterations: Infinity});
+
+var player4 = target4.animate([
+  {transform: 'none', background: 'blue'},
+  {transform: 'rotate(90deg)', background: 'blue'}
+], {duration: 1000, iterations: Infinity});
+
+setInterval(function() {
+  var playbackRate = (Math.random() - 0.5) * 5;
+  player1.playbackRate = playbackRate;
+  player2.playbackRate = playbackRate;
+  player3.playbackRate = playbackRate;
+  player4.playbackRate = playbackRate;
+}, 100);
+</script>