Add TransitionInterpolation class for CSS Transition refactor

third_party/WebKit/Source/core/animation/InterpolableValue.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 InterpolableValue_h
 #define InterpolableValue_h
 
 #include "core/CoreExport.h"
 #include "core/animation/animatable/AnimatableValue.h"
 #include "platform/heap/Handle.h"
@@ skipping 21 matching lines @@
   virtual std::unique_ptr<InterpolableValue> cloneAndZero() const = 0;
   virtual void scale(double scale) = 0;
   virtual void scaleAndAdd(double scale, const InterpolableValue& other) = 0;
 
  private:
   virtual void interpolate(const InterpolableValue& to,
                            const double progress,
                            InterpolableValue& result) const = 0;
 
   friend class LegacyStyleInterpolation;
+  friend class TransitionInterpolation;
   friend class PairwisePrimitiveInterpolation;
 
   // Keep interpolate private, but allow calls within the hierarchy without
   // knowledge of type.
   friend class InterpolableNumber;
   friend class InterpolableBool;
   friend class InterpolableList;
 
   friend class AnimationInterpolableValueTest;
 };
@@ skipping 126 matching lines @@
                   value.isList());
 DEFINE_TYPE_CASTS(InterpolableAnimatableValue,
                   InterpolableValue,
                   value,
                   value->isAnimatableValue(),
                   value.isAnimatableValue());
 
 }  // namespace blink
 
 #endif