Add foundation for removing AnimatableValues from StyleInterpolation

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 "platform/heap/Handle.h"
 
 namespace blink {
 
 class PropertyHandle;
 
 class CORE_EXPORT Interpolation : public RefCountedWillBeGarbageCollectedFinalized<Interpolation> {
 public:
     virtual ~Interpolation();
 
-    void interpolate(int iteration, double fraction) const;
+    virtual void interpolate(int iteration, double fraction);
 
     virtual bool isStyleInterpolation() const { return false; }
+    virtual bool isInvalidatableStyleInterpolation() const { return false; }
     virtual bool isLegacyStyleInterpolation() const { return false; }
     virtual bool isSVGInterpolation() const { return false; }
 
     virtual PropertyHandle property() const = 0;
 
     DECLARE_VIRTUAL_TRACE();
 
 protected:
     const OwnPtrWillBeMember<InterpolableValue> m_start;
     const OwnPtrWillBeMember<InterpolableValue> m_end;
@@ skipping 11 matching lines @@
     friend class AnimationInterpolationEffectTest;
     friend class AnimationDoubleStyleInterpolationTest;
     friend class AnimationVisibilityStyleInterpolationTest;
     friend class AnimationColorStyleInterpolationTest;
     friend class AnimationSVGStrokeDasharrayStyleInterpolationTest;
 };
 
 } // namespace blink
 
 #endif // Interpolation_h