Implemented additive animations for length

Source/core/animation/InterpolationPipeline.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef InterpolationPipeline_h
+#define InterpolationPipeline_h
+
+#include "core/animation/InterpolationPipelineStage.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class InterpolationPipeline : public RefCountedWillBeGarbageCollected<InterpolationPipeline> {
+public:
+    static PassRefPtrWillBeRawPtr<InterpolationPipeline> create()
+    {
+        return adoptRefWillBeNoop(new InterpolationPipeline());
+    }
+
+    RefPtrWillBeRawPtr<InterpolationPipelineStage> first() const
+    {
+        return m_first;
+    }
+
+    RefPtrWillBeRawPtr<InterpolationPipelineStage> last() const
+    {
+        return m_last;
+    }
+
+    void append(PassRefPtrWillBeRawPtr<InterpolationPipelineStage>);
+    bool isEmpty() const { return !m_first && !m_last; }
+
+    void trace(Visitor* visitor)
+    {
+        m_first->trace(visitor);
+        m_last->trace(visitor);
+    }
+
+    ~InterpolationPipeline()
+    {
+    }
+private:
+    InterpolationPipeline()
+        : m_first(nullptr)
+        , m_last(nullptr)
+    {
+    }
+
+    RefPtrWillBeMember<InterpolationPipelineStage> m_first;
+    RefPtrWillBeMember<InterpolationPipelineStage> m_last;
+};
+
+using InterpolationPipelineMap = WillBeHeapHashMap<CSSPropertyID, RefPtrWillBeRawPtr<InterpolationPipeline>>;
+
+} // namespace blink
+
+#endif // InterpolationPipeline_h