Implemented additive animations for length

Source/core/animation/AnimationStack.cpp

Index: Source/core/animation/AnimationStack.cpp
diff --git a/Source/core/animation/AnimationStack.cpp b/Source/core/animation/AnimationStack.cpp
index 178d1d9013beb52df4df83a6bc2de26632b46eca..071481f12e468d4349c52a2818d0b1c7d7a20e2b 100644
--- a/Source/core/animation/AnimationStack.cpp
+++ b/Source/core/animation/AnimationStack.cpp
@@ -42,10 +42,20 @@ namespace blink {
 
 namespace {
 
-void copyToActiveInterpolationMap(const WillBeHeapVector<RefPtrWillBeMember<blink::Interpolation> >& source, WillBeHeapHashMap<CSSPropertyID, RefPtrWillBeMember<blink::Interpolation> >& target)
+void copyToActiveInterpolationMap(const WillBeHeapVector<RefPtrWillBeMember<blink::Interpolation>>& source, InterpolationPipelineMap& target)
 {
     for (const auto& interpolation : source) {
-        target.set(toStyleInterpolation(interpolation.get())->id(), interpolation.get());
+        CSSPropertyID property = toStyleInterpolation(interpolation.get())->id();
+
+        RefPtrWillBeRawPtr<InterpolationPipelineStage> newStage = InterpolationPipelineStage::create(interpolation);
+
+        RefPtrWillBeRawPtr<InterpolationPipeline> pipeline = target.get(property);
+        if (!pipeline) {
+            pipeline = InterpolationPipeline::create();
+            target.set(property, pipeline);
+        }
+
+        pipeline->append(newStage);
     }
 }
 
@@ -55,7 +65,7 @@ bool compareEffects(const OwnPtrWillBeMember<SampledEffect>& effect1, const OwnP
     return effect1->sequenceNumber() < effect2->sequenceNumber();
 }
 
-void copyNewAnimationsToActiveInterpolationMap(const WillBeHeapVector<RawPtrWillBeMember<InertAnimation> >& newAnimations, WillBeHeapHashMap<CSSPropertyID, RefPtrWillBeMember<Interpolation> >& result)
+void copyNewAnimationsToActiveInterpolationMap(const WillBeHeapVector<RawPtrWillBeMember<InertAnimation>>& newAnimations, InterpolationPipelineMap& result)
 {
     for (const auto& newAnimation : newAnimations) {
         OwnPtrWillBeRawPtr<WillBeHeapVector<RefPtrWillBeMember<Interpolation>>> sample = nullptr;
@@ -89,14 +99,14 @@ bool AnimationStack::hasActiveAnimationsOnCompositor(CSSPropertyID property) con
     return false;
 }
 
-WillBeHeapHashMap<CSSPropertyID, RefPtrWillBeMember<Interpolation> > AnimationStack::activeInterpolations(AnimationStack* animationStack, const WillBeHeapVector<RawPtrWillBeMember<InertAnimation> >* newAnimations, const WillBeHeapHashSet<RawPtrWillBeMember<const AnimationPlayer> >* suppressedAnimationPlayers, Animation::Priority priority, double timelineCurrentTime)
+InterpolationPipelineMap AnimationStack::activeInterpolations(AnimationStack* animationStack, const WillBeHeapVector<RawPtrWillBeMember<InertAnimation>>* newAnimations, const WillBeHeapHashSet<RawPtrWillBeMember<const AnimationPlayer>>* suppressedAnimationPlayers, Animation::Priority priority, double timelineCurrentTime)
 {
     // We don't exactly know when new animations will start, but timelineCurrentTime is a good estimate.
 
-    WillBeHeapHashMap<CSSPropertyID, RefPtrWillBeMember<Interpolation> > result;
+    InterpolationPipelineMap result;
 
     if (animationStack) {
-        WillBeHeapVector<OwnPtrWillBeMember<SampledEffect> >& effects = animationStack->m_effects;
+        WillBeHeapVector<OwnPtrWillBeMember<SampledEffect>>& effects = animationStack->m_effects;
         // std::sort doesn't work with OwnPtrs
         nonCopyingSort(effects.begin(), effects.end(), compareEffects);
         animationStack->simplifyEffects();