Web Animations CSS: Snapshot missing start/end Keyframes and remove duplicates

Source/core/animation/KeyframeAnimationEffect.h

Index: Source/core/animation/KeyframeAnimationEffect.h
diff --git a/Source/core/animation/KeyframeAnimationEffect.h b/Source/core/animation/KeyframeAnimationEffect.h
index 14985b9c1802bb0ee008bac027544cf2926e2506..fccd2c733d1cb3763b21cd7ad8e345609f5e67b8 100644
--- a/Source/core/animation/KeyframeAnimationEffect.h
+++ b/Source/core/animation/KeyframeAnimationEffect.h
@@ -51,6 +51,10 @@ public:
     {
         return adoptRef(new Keyframe);
     }
+    static bool compareOffsets(const RefPtr<Keyframe>& a, const RefPtr<Keyframe>& b)
+    {
+        return a->offset() < b->offset();
+    }
     void setOffset(double offset) { m_offset = offset; }
     double offset() const { return m_offset; }
     void setComposite(AnimationEffect::CompositeOperation composite) { m_composite = composite; }