Add CSSInterpolationType specific ConversionChecker

third_party/WebKit/Source/core/animation/CSSInterpolationType.h

Index: third_party/WebKit/Source/core/animation/CSSInterpolationType.h
diff --git a/third_party/WebKit/Source/core/animation/CSSInterpolationType.h b/third_party/WebKit/Source/core/animation/CSSInterpolationType.h
index f475404dc6619ce6348dd70c24d6eebc67e18c7c..7e72a404bb55c747a63f9ca633ecb84e488b6c15 100644
--- a/third_party/WebKit/Source/core/animation/CSSInterpolationType.h
+++ b/third_party/WebKit/Source/core/animation/CSSInterpolationType.h
@@ -17,6 +17,18 @@ class CSSInterpolationType : public InterpolationType {
  public:
   void SetCustomPropertyRegistration(const PropertyRegistration&);
 
+  class CSSConversionChecker : public ConversionChecker {
+   public:
+    bool IsValid(const InterpolationEnvironment& environment,
+                 const InterpolationValue& underlying) const final {
+      return IsValid(environment.GetState(), underlying);
+    }
+
+   protected:
+    virtual bool IsValid(const StyleResolverState&,
+                         const InterpolationValue& underlying) const = 0;
+  };
+
  protected:
   CSSInterpolationType(PropertyHandle);