Web Animations: define distance for AnimatableColor

Source/core/animation/AnimatableColor.h

Index: Source/core/animation/AnimatableColor.h
diff --git a/Source/core/animation/AnimatableColor.h b/Source/core/animation/AnimatableColor.h
index e5fc028828137b7af68a269920c6e7e7e92a996b..b8c62f5aa9ef44b646631915fd61e722b2939d62 100644
--- a/Source/core/animation/AnimatableColor.h
+++ b/Source/core/animation/AnimatableColor.h
@@ -44,6 +44,7 @@ public:
     AnimatableColorImpl interpolateTo(const AnimatableColorImpl&, double fraction) const;
     AnimatableColorImpl addWith(const AnimatableColorImpl&) const;
     bool operator==(const AnimatableColorImpl&) const;
+    double distanceTo(const AnimatableColorImpl&) const;
 
 private:
     float m_alpha;
@@ -74,6 +75,7 @@ private:
     }
     virtual AnimatableType type() const OVERRIDE { return TypeColor; }
     virtual bool equalTo(const AnimatableValue*) const OVERRIDE;
+    virtual double distanceTo(const AnimatableValue*) const OVERRIDE;
     const AnimatableColorImpl m_color;
     const AnimatableColorImpl m_visitedLinkColor;
 };