Revert of Web Animations: Remove AnimationPlayer discarding logic

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 8e0fab0c9e622455bb27b5d232d2971d5ecc74b9..dea3c9c8916bce68fe8b10395f4a625bc669c697 100644
--- a/Source/core/animation/AnimationStack.cpp
+++ b/Source/core/animation/AnimationStack.cpp
@@ -90,6 +90,7 @@
         WillBeHeapVector<OwnPtrWillBeMember<SampledEffect> >& effects = animationStack->m_effects;
         // std::sort doesn't work with OwnPtrs
         nonCopyingSort(effects.begin(), effects.end(), compareEffects);
+        animationStack->simplifyEffects();
         for (const auto& effect : effects) {
             if (effect->priority() != priority || (suppressedAnimationPlayers && effect->animation() && suppressedAnimationPlayers->contains(effect->animation()->player())))
                 continue;
@@ -101,6 +102,32 @@
         copyNewAnimationsToActiveInterpolationMap(*newAnimations, result);
 
     return result;
+}
+
+void AnimationStack::simplifyEffects()
+{
+    // FIXME: This will need to be updated when we have 'add' keyframes.
+
+    BitArray<numCSSProperties> replacedProperties;
+    for (size_t i = m_effects.size(); i--; ) {
+        SampledEffect& effect = *m_effects[i];
+        effect.removeReplacedInterpolationsIfNeeded(replacedProperties);
+        if (!effect.canChange()) {
+            for (const auto& interpolation : effect.interpolations())
+                replacedProperties.set(toStyleInterpolation(interpolation.get())->id());
+        }
+    }
+
+    size_t dest = 0;
+    for (auto& effect : m_effects) {
+        if (!effect->interpolations().isEmpty()) {
+            m_effects[dest++].swap(effect);
+            continue;
+        }
+        if (effect->animation())
+            effect->animation()->notifySampledEffectRemovedFromAnimationStack();
+    }
+    m_effects.shrink(dest);
 }
 
 DEFINE_TRACE(AnimationStack)