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+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Animation.playbackRate</title>
+<link rel="help" href="https://w3c.github.io/web-animations/#dom-animation-playbackrate">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../../testcommon.js"></script>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+function assert_playbackrate(animation,
+                             previousAnimationCurrentTime,
+                             previousTimelineCurrentTime,
+                             description) {
+  var accuracy = 0.001; /* accuracy of DOMHighResTimeStamp */
+  var animationCurrentTimeDifference =
+    animation.currentTime - previousAnimationCurrentTime;
+  var timelineCurrentTimeDifference =
+    animation.timeline.currentTime - previousTimelineCurrentTime;
+
+  assert_approx_equals(animationCurrentTimeDifference,
+                       timelineCurrentTimeDifference * animation.playbackRate,
+                       accuracy,
+                       description);
+}
+
+promise_test(function(t) {
+  var div = createDiv(t);
+  var animation = div.animate(null, 100 * MS_PER_SEC);
+  return animation.ready.then(function() {
+    animation.currentTime = 7 * MS_PER_SEC; // ms
+    animation.playbackRate = 0.5;
+
+    assert_equals(animation.currentTime, 7 * MS_PER_SEC,
+      'Reducing Animation.playbackRate should not change the currentTime ' +
+      'of a playing animation');
+    animation.playbackRate = 2;
+    assert_equals(animation.currentTime, 7 * MS_PER_SEC,
+      'Increasing Animation.playbackRate should not change the currentTime ' +
+      'of a playing animation');
+  });
+}, 'Test the initial effect of setting playbackRate on currentTime');
+
+promise_test(function(t) {
+  var div = createDiv(t);
+  var animation = div.animate(null, 100 * MS_PER_SEC);
+  animation.playbackRate = 2;
+  var previousTimelineCurrentTime;
+  var previousAnimationCurrentTime;
+  return animation.ready.then(function() {
+    previousAnimationCurrentTime = animation.currentTime;
+    previousTimelineCurrentTime = animation.timeline.currentTime;
+    return waitForAnimationFrames(1);
+  }).then(function() {
+    assert_playbackrate(animation,
+      previousAnimationCurrentTime,
+      previousTimelineCurrentTime,
+      'animation.currentTime should be 2 times faster than timeline.');
+  });
+}, 'Test the effect of setting playbackRate on currentTime');
+
+promise_test(function(t) {
+  var div = createDiv(t);
+  var animation = div.animate(null, 100 * MS_PER_SEC);
+  animation.playbackRate = 2;
+  var previousTimelineCurrentTime;
+  var previousAnimationCurrentTime;
+  return animation.ready.then(function() {
+    previousAnimationCurrentTime = animation.currentTime;
+    previousTimelineCurrentTime = animation.timeline.currentTime;
+    animation.playbackRate = 1;
+    return waitForAnimationFrames(1);
+  }).then(function() {
+    assert_equals(animation.playbackRate, 1,
+      'sanity check: animation.playbackRate is still 1.');
+    assert_playbackrate(animation,
+      previousAnimationCurrentTime,
+      previousTimelineCurrentTime,
+      'animation.currentTime should be the same speed as timeline now.');
+  });
+}, 'Test the effect of setting playbackRate while playing animation');
+
+</script>
+</body>