Implemented additive animations for length

Source/core/animation/StringKeyframe.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 StringKeyframe_h
 #define StringKeyframe_h
 
 #include "core/animation/Keyframe.h"
 #include "core/css/StylePropertySet.h"
 
@@ skipping 33 matching lines @@
         virtual void trace(Visitor*) override;
 
     private:
         PropertySpecificKeyframe(double offset, PassRefPtr<TimingFunction> easing, CSSValue*);
 
         virtual PassOwnPtrWillBeRawPtr<Keyframe::PropertySpecificKeyframe> cloneWithOffset(double offset) const;
         virtual bool isStringPropertySpecificKeyframe() const override { return true; }
 
         static bool createInterpolationsFromCSSValues(CSSPropertyID, CSSValue* fromCSSValue, CSSValue* toCSSValue, Element*, OwnPtrWillBeRawPtr<WillBeHeapVector<RefPtrWillBeMember<Interpolation>>>& interpolations);
 
-        void ensureAnimatableValueCaches(CSSPropertyID, Keyframe::PropertySpecificKeyframe&, Element*, CSSValue& fromCSSValue, CSSValue& toCSSValue) const;
-
         RefPtrWillBeMember<CSSValue> m_value;
         mutable RefPtrWillBeMember<AnimatableValue> m_animatableValueCache;
     };
 
 private:
     StringKeyframe()
         : m_propertySet(MutableStylePropertySet::create())
     { }
 
     StringKeyframe(const StringKeyframe& copyFrom);
 
     virtual PassRefPtrWillBeRawPtr<Keyframe> clone() const override;
     virtual PassOwnPtrWillBeRawPtr<Keyframe::PropertySpecificKeyframe> createPropertySpecificKeyframe(CSSPropertyID) const override;
 
     virtual bool isStringKeyframe() const override { return true; }
 
     RefPtrWillBeMember<MutableStylePropertySet> m_propertySet;
 };
 
 using StringPropertySpecificKeyframe = StringKeyframe::PropertySpecificKeyframe;
 
 DEFINE_TYPE_CASTS(StringKeyframe, Keyframe, value, value->isStringKeyframe(), value.isStringKeyframe());
 DEFINE_TYPE_CASTS(StringPropertySpecificKeyframe, Keyframe::PropertySpecificKeyframe, value, value->isStringPropertySpecificKeyframe(), value.isStringPropertySpecificKeyframe());
 
 }
 
 #endif