Implemented additive animations for length

Source/core/animation/StyleInterpolation.h

 // Copyright 2014 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 StyleInterpolation_h
 #define StyleInterpolation_h
 
 #include "core/CSSPropertyNames.h"
 #include "core/animation/Interpolation.h"
 
@@ skipping 16 matching lines @@
 class StyleInterpolation : public Interpolation {
 public:
     // 1) convert m_cachedValue into an X
     // 2) shove X into StyleResolverState
     // X can be:
     // (1) a CSSValue (and applied via StyleBuilder::applyProperty)
     // (2) an AnimatableValue (and applied via // AnimatedStyleBuilder::applyProperty)
     // (3) a custom value that is inserted directly into the StyleResolverState.
     virtual void apply(StyleResolverState&) const = 0;
 
+    // FIXME: Make abstract
+    virtual void apply(StyleResolverState& state, const InterpolableValue&) const { apply(state); }
+
     virtual bool isStyleInterpolation() const override final { return true; }
 
     CSSPropertyID id() const { return m_id; }
 
     virtual void trace(Visitor* visitor) override
     {
         Interpolation::trace(visitor);
     }
 
 protected:
     CSSPropertyID m_id;
 
     StyleInterpolation(PassOwnPtrWillBeRawPtr<InterpolableValue> start, PassOwnPtrWillBeRawPtr<InterpolableValue> end, CSSPropertyID id)
         : Interpolation(start, end)
         , m_id(id)
     {
     }
+
+    StyleInterpolation(PassOwnPtrWillBeRawPtr<InterpolableValue> start, PassOwnPtrWillBeRawPtr<InterpolableValue> end, CSSPropertyID id, AnimationEffect::CompositeOperation compositeStart, AnimationEffect::CompositeOperation compositeEnd)
+        : Interpolation(start, end, compositeStart, compositeEnd)
+        , m_id(id)
+    {
+    }
 };
 
 DEFINE_TYPE_CASTS(StyleInterpolation, Interpolation, value, value->isStyleInterpolation(), value.isStyleInterpolation());
 
 }
 
 #endif