[ScrollTimeline] Add previously finished animation to pending on restart

Previously when scroll-linked animation goes from finished to running we
did not add it to pending animations. As a result it never got restarted
on the compositor. See crbug.com/1070635 for more details.

Bug: 1070635
Change-Id: I1454bfbc75f8ce07dc952645c51fabd3804ef0d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2218749Reviewed-by: Kevin Ellis <kevers@chromium.org>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773183}

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

@@ -1361,6 +1361,11 @@ void Animation::UpdateFinishedState(UpdateType update_type,
         ScheduleAsyncFinish();
     }
   } else {
+    // Previously finished animation may restart so they should be added to
+    // pending animations to make sure that a compositor animation is re-created
+    // during future PreCommit.
+    if (finished_)
+      SetCompositorPending();
     // 6. If not finished but the current finished promise is already resolved,
     //    create a new promise.
     finished_ = pending_finish_notification_ = committed_finish_notification_ =

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

@@ -1602,6 +1602,90 @@ TEST_F(AnimationAnimationTestNoCompositing, ScrollLinkedAnimationCreation) {
   EXPECT_EQ(40, scroll_animation->currentTime());
 }
 
+// Verifies that finished composited scroll-linked animations restart on
+// compositor upon reverse scrolling.
+TEST_F(AnimationAnimationTestCompositing,
+       FinishedScrollLinkedAnimationRestartsOnReverseScrolling) {
+  ResetWithCompositedAnimation();
+  SetBodyInnerHTML(R"HTML(
+    <style>
+      #scroller { will-change: transform; overflow: scroll; width: 100px; height: 100px; }
+      #target { width: 100px; height: 200px; will-change: opacity;}
+      #spacer { width: 200px; height: 700px; }
+    </style>
+    <div id ='scroller'>
+      <div id ='target'></div>
+      <div id ='spacer'></div>
+    </div>
+  )HTML");
+
+  LayoutBoxModelObject* scroller =
+      ToLayoutBoxModelObject(GetLayoutObjectByElementId("scroller"));
+  ASSERT_TRUE(scroller->UsesCompositedScrolling());
+
+  // Create ScrollTimeline
+  ScrollTimelineOptions* options = ScrollTimelineOptions::Create();
+  DoubleOrScrollTimelineAutoKeyword time_range =
+      DoubleOrScrollTimelineAutoKeyword::FromDouble(100);
+  options->setTimeRange(time_range);
+  options->setScrollSource(GetElementById("scroller"));
+  ScrollTimeline* scroll_timeline =
+      ScrollTimeline::Create(GetDocument(), options, ASSERT_NO_EXCEPTION);
+
+  // Create KeyframeEffect
+  Timing timing;
+  timing.iteration_duration = AnimationTimeDelta::FromSecondsD(30);
+  Persistent<StringKeyframe> start_keyframe =
+      MakeGarbageCollected<StringKeyframe>();
+  start_keyframe->SetCSSPropertyValue(CSSPropertyID::kOpacity, "1.0",
+                                      SecureContextMode::kInsecureContext,
+                                      nullptr);
+  Persistent<StringKeyframe> end_keyframe =
+      MakeGarbageCollected<StringKeyframe>();
+  end_keyframe->SetCSSPropertyValue(CSSPropertyID::kOpacity, "0.0",
+                                    SecureContextMode::kInsecureContext,
+                                    nullptr);
+
+  StringKeyframeVector keyframes;
+  keyframes.push_back(start_keyframe);
+  keyframes.push_back(end_keyframe);
+
+  Element* element = GetElementById("target");
+  auto* model = MakeGarbageCollected<StringKeyframeEffectModel>(keyframes);
+
+  KeyframeEffect* keyframe_effect =
+      MakeGarbageCollected<KeyframeEffect>(element, model, timing);
+
+  // Create scroll-linked animation
+  NonThrowableExceptionState exception_state;
+  Animation* scroll_animation =
+      Animation::Create(keyframe_effect, scroll_timeline, exception_state);
+  model->SnapshotAllCompositorKeyframesIfNecessary(
+      *element, *ComputedStyle::Create(), nullptr);
+  UpdateAllLifecyclePhasesForTest();
+
+  scroll_animation->play();
+  EXPECT_EQ(scroll_animation->playState(), "running");
+  GetDocument().GetPendingAnimations().Update(nullptr, true);
+  EXPECT_TRUE(scroll_animation->HasActiveAnimationsOnCompositor());
+
+  // Advances the animation to "finished" state. The composited animation will
+  // be destroyed accordingly.
+  scroll_animation->setCurrentTime(50000);
+  EXPECT_EQ(scroll_animation->playState(), "finished");
+  scroll_animation->Update(kTimingUpdateForAnimationFrame);
+  GetDocument().GetPendingAnimations().Update(nullptr, true);
+  EXPECT_FALSE(scroll_animation->HasActiveAnimationsOnCompositor());
+
+  // Restarting the animation should create a new compositor animation.
+  scroll_animation->setCurrentTime(100);
+  UpdateAllLifecyclePhasesForTest();
+  EXPECT_EQ(scroll_animation->playState(), "running");
+  scroll_animation->Update(kTimingUpdateForAnimationFrame);
+  GetDocument().GetPendingAnimations().Update(nullptr, true);
+  EXPECT_TRUE(scroll_animation->HasActiveAnimationsOnCompositor());
+}
+
 TEST_F(AnimationAnimationTestNoCompositing,
        RemoveCanceledAnimationFromActiveSet) {
   EXPECT_EQ("running", animation->playState());