Perform a microtask checkpoint after updating timelines.

Updating timelines can enqueue tasks related to ready and finish
promises which should run before animation events and updated
rendering.

Bug: 1116020
Change-Id: Ica1927bb3921eef574abeaca23bb198dda658ccd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354164Reviewed-by: Kevin Ellis <kevers@chromium.org>
Commit-Queue: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798259}

third_party/blink/renderer/core/animation/document_animations.cc

@@ -42,6 +42,7 @@
 #include "third_party/blink/renderer/core/frame/local_frame_view.h"
 #include "third_party/blink/renderer/core/page/page.h"
 #include "third_party/blink/renderer/core/page/page_animator.h"
+#include "third_party/blink/renderer/platform/bindings/microtask.h"
 
 namespace blink {
 
@@ -73,6 +74,14 @@ void DocumentAnimations::AddTimeline(AnimationTimeline& timeline) {
 
 void DocumentAnimations::UpdateAnimationTimingForAnimationFrame() {
   UpdateAnimationTiming(*document_, timelines_, kTimingUpdateForAnimationFrame);
+
+  // Perform a microtask checkpoint per step 3 of
+  // https://drafts.csswg.org/web-animations-1/#timelines. This is to
+  // ensure that any microtasks queued up as a result of resolving or
+  // rejecting Promise objects as part of updating timelines run their
+  // callbacks prior to dispatching animation events and generating
+  // the next main frame.
+  Microtask::PerformCheckpoint(V8PerIsolateData::MainThreadIsolate());
 }
 
 bool DocumentAnimations::NeedsAnimationTimingUpdate() {

third_party/blink/web_tests/external/wpt/scroll-animations/scroll-animation.html

@@ -198,6 +198,11 @@ promise_test(async t => {
 
     scroller.scrollTop = maxScroll;
     await animation.finished;
+
+    // Wait for next frame to allow the animation to send finish events. The
+    // finished promise fires before events are sent.
+    await waitForNextFrame();
+
     assert_true(sent_finish_event,
                  "Animation finished event is sent on reaching max scroll.");
 }, 'Sending animation finished events by finished animation on reverse ' +

third_party/blink/web_tests/external/wpt/web-animations/timing-model/timelines/timelines.html

@@ -5,6 +5,12 @@
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script src="../../testcommon.js"></script>
+<style>
+@keyframes opacity-animation {
+  from { opacity: 1; }
+  to { opacity: 0; }
+}
+</style>
 <div id="log"></div>
 <script>
 'use strict';
@@ -84,4 +90,23 @@ async_test(t => {
   }));
 }, 'Performs a microtask checkpoint after updating timelins');
 
+async_test(t => {
+  const div = createDiv(t);
+  let readyPromiseRan = false;
+  let finishedPromiseRan = false;
+  div.style.animation = 'opacity-animation 1ms';
+  let anim = div.getAnimations()[0];
+  anim.ready.then(t.step_func(() => {
+    readyPromiseRan = true;
+  }));
+  div.addEventListener('animationstart', t.step_func(() => {
+    assert_true(readyPromiseRan, 'It should run ready promise before animationstart event');
+  }));
+  anim.finished.then(t.step_func(() => {
+    finishedPromiseRan = true;
+  }));
+  div.addEventListener('animationend', t.step_func_done(() => {
+    assert_true(finishedPromiseRan, 'It should run finished promise before animationend event');
+  }));
+}, 'Runs finished promise before animation events');
 </script>

third_party/blink/web_tests/external/wpt/web-animations/timing-model/timelines/update-and-send-events-replacement-expected.txt

@@ -38,7 +38,7 @@ PASS Does NOT remove an animation after making a redundant change to another ani
 PASS Does NOT remove an animation after making a redundant change to its effect's properties
 FAIL Updates ALL timelines before checking for replacement promise_test: Unhandled rejection with value: object "TypeError: Cannot set property timeline of #<Animation> which has only a getter"
 PASS Dispatches remove events after finish events
-FAIL Fires remove event before requestAnimationFrame assert_true: Not expecting event, but got remove event expected true got false
+PASS Fires remove event before requestAnimationFrame
 PASS Queues all remove events before running them
 PASS Performs removal in deeply nested iframes
 Harness: the test ran to completion.