Implemented additive animations for length

Source/core/animation/css/CSSAnimations.cpp

Index: Source/core/animation/css/CSSAnimations.cpp
diff --git a/Source/core/animation/css/CSSAnimations.cpp b/Source/core/animation/css/CSSAnimations.cpp
index 7ca241a49405e2f544fe2611b1400edd229aeb11..ff5dda054d3f2f4197cbc15cc001fd1340dbbc31 100644
--- a/Source/core/animation/css/CSSAnimations.cpp
+++ b/Source/core/animation/css/CSSAnimations.cpp
@@ -594,7 +594,7 @@ void CSSAnimations::calculateAnimationActiveInterpolations(CSSAnimationUpdate* u
     AnimationStack* animationStack = activeAnimations ? &activeAnimations->defaultStack() : nullptr;
 
     if (update->newAnimations().isEmpty() && update->suppressedAnimationAnimationPlayers().isEmpty()) {
-        WillBeHeapHashMap<CSSPropertyID, RefPtrWillBeMember<Interpolation>> activeInterpolationsForAnimations(AnimationStack::activeInterpolations(animationStack, 0, 0, Animation::DefaultPriority, timelineCurrentTime));
+        InterpolationPipelineMap activeInterpolationsForAnimations(AnimationStack::activeInterpolations(animationStack, 0, 0, Animation::DefaultPriority, timelineCurrentTime));
         update->adoptActiveInterpolationsForAnimations(activeInterpolationsForAnimations);
         return;
     }
@@ -605,7 +605,7 @@ void CSSAnimations::calculateAnimationActiveInterpolations(CSSAnimationUpdate* u
     for (const auto& updatedAnimation : update->animationsWithUpdates())
         newAnimations.append(updatedAnimation.animation.get()); // Animations with updates use a temporary InertAnimation for the current frame.
 
-    WillBeHeapHashMap<CSSPropertyID, RefPtrWillBeMember<Interpolation>> activeInterpolationsForAnimations(AnimationStack::activeInterpolations(animationStack, &newAnimations, &update->suppressedAnimationAnimationPlayers(), Animation::DefaultPriority, timelineCurrentTime));
+    InterpolationPipelineMap activeInterpolationsForAnimations(AnimationStack::activeInterpolations(animationStack, &newAnimations, &update->suppressedAnimationAnimationPlayers(), Animation::DefaultPriority, timelineCurrentTime));
     update->adoptActiveInterpolationsForAnimations(activeInterpolationsForAnimations);
 }
 
@@ -614,7 +614,7 @@ void CSSAnimations::calculateTransitionActiveInterpolations(CSSAnimationUpdate*
     ActiveAnimations* activeAnimations = animatingElement ? animatingElement->activeAnimations() : nullptr;
     AnimationStack* animationStack = activeAnimations ? &activeAnimations->defaultStack() : nullptr;
 
-    WillBeHeapHashMap<CSSPropertyID, RefPtrWillBeMember<Interpolation>> activeInterpolationsForTransitions;
+    InterpolationPipelineMap activeInterpolationsForTransitions;
     if (update->newTransitions().isEmpty() && update->cancelledTransitions().isEmpty()) {
         activeInterpolationsForTransitions = AnimationStack::activeInterpolations(animationStack, 0, 0, Animation::TransitionPriority, timelineCurrentTime);
     } else {