Add TransitionInterpolation class for CSS Transition refactor

third_party/WebKit/Source/core/animation/Interpolation.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 Interpolation_h
 #define Interpolation_h
 
 #include "core/CoreExport.h"
 #include "core/animation/InterpolableValue.h"
 #include "wtf/Forward.h"
 #include "wtf/RefCounted.h"
 #include <memory>
 
 namespace blink {
 
 class PropertyHandle;
 
 // Represents an animation's effect between an adjacent pair of
 // PropertySpecificKeyframes.
 class CORE_EXPORT Interpolation : public RefCounted<Interpolation> {
   WTF_MAKE_NONCOPYABLE(Interpolation);
 
  public:
   virtual ~Interpolation() {}
 
   virtual void interpolate(int iteration, double fraction) = 0;
 
   virtual bool isInvalidatableInterpolation() const { return false; }
   virtual bool isLegacyStyleInterpolation() const { return false; }
+  virtual bool isTransitionInterpolation() const { return false; }
 
   virtual const PropertyHandle& getProperty() const = 0;
   virtual bool dependsOnUnderlyingValue() const { return false; }
 
  protected:
   Interpolation() {}
 };
 
 using ActiveInterpolations = Vector<RefPtr<Interpolation>, 1>;
 
 }  // namespace blink
 
 #endif  // Interpolation_h