Web Animations: define distance for AnimatableColor

Source/core/animation/AnimatableDouble.cpp

Index: Source/core/animation/AnimatableDouble.cpp
diff --git a/Source/core/animation/AnimatableDouble.cpp b/Source/core/animation/AnimatableDouble.cpp
index c49c3bd0cc471bd82856beac2731aabd4022af84..77d80f71ad2c6dd46a2342d50d1cd205d5431008 100644
--- a/Source/core/animation/AnimatableDouble.cpp
+++ b/Source/core/animation/AnimatableDouble.cpp
@@ -34,6 +34,7 @@
 #include "core/css/CSSPrimitiveValue.h"
 #include "core/css/CSSValuePool.h"
 #include "platform/animation/AnimationUtilities.h"
+#include <math.h>
 
 namespace WebCore {
 
@@ -74,4 +75,10 @@ bool AnimatableDouble::equalTo(const AnimatableValue* value) const
     return m_number == toAnimatableDouble(value)->m_number;
 }
 
+double AnimatableDouble::distanceTo(const AnimatableValue* value) const
+{
+    const AnimatableDouble* other = toAnimatableDouble(value);
+    return fabs(m_number - other->m_number);
+}
+
 } // namespace WebCore