Web Animations CSS: Assert underlying value is not used

Source/core/animation/AnimationEffect.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 34 matching lines @@
     enum CompositeOperation {
         CompositeReplace,
         CompositeAdd,
     };
     // Encapsulates the value which results from applying a set of composition operations onto an
     // underlying value. It is used to represent the output of the effect phase of the Web
     // Animations model.
     class CompositableValue : public RefCounted<CompositableValue> {
     public:
         virtual ~CompositableValue() { }
+        virtual bool dependsOnUnderlyingValue() const = 0;
         virtual PassRefPtr<AnimatableValue> compositeOnto(const AnimatableValue*) const = 0;
     };
 
     virtual ~AnimationEffect() { }
     typedef HashMap<CSSPropertyID, RefPtr<CompositableValue> > CompositableValueMap;
     virtual PassOwnPtr<CompositableValueMap> sample(int iteration, double fraction) const = 0;
 };
 
 } // namespace WebCore
 
 #endif // AnimationEffect_h