Add TransitionKeyframe class for CSS Transition refactor

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

Index: third_party/WebKit/Source/core/animation/InterpolationType.h
diff --git a/third_party/WebKit/Source/core/animation/InterpolationType.h b/third_party/WebKit/Source/core/animation/InterpolationType.h
index d11a8af2c7175b13af6f0f6bbc3d4b75c28d7db5..8eec9e26282f50c1b2a6650319b6c98199f73882 100644
--- a/third_party/WebKit/Source/core/animation/InterpolationType.h
+++ b/third_party/WebKit/Source/core/animation/InterpolationType.h
@@ -80,6 +80,16 @@ class InterpolationType {
   virtual InterpolationValue maybeConvertUnderlyingValue(
       const InterpolationEnvironment&) const = 0;
 
+  virtual PairwiseInterpolationValue maybeMergeSingles(
+      InterpolationValue&& start,
+      InterpolationValue&& end) const {
+    DCHECK(!start.nonInterpolableValue);
+    DCHECK(!end.nonInterpolableValue);
+    return PairwiseInterpolationValue(std::move(start.interpolableValue),
+                                      std::move(end.interpolableValue),
+                                      nullptr);
+  }
+
   virtual void composite(UnderlyingValueOwner& underlyingValueOwner,
                          double underlyingFraction,
                          const InterpolationValue& value,
@@ -106,16 +116,6 @@ class InterpolationType {
  protected:
   InterpolationType(PropertyHandle property) : m_property(property) {}
 
-  virtual PairwiseInterpolationValue maybeMergeSingles(
-      InterpolationValue&& start,
-      InterpolationValue&& end) const {
-    DCHECK(!start.nonInterpolableValue);
-    DCHECK(!end.nonInterpolableValue);
-    return PairwiseInterpolationValue(std::move(start.interpolableValue),
-                                      std::move(end.interpolableValue),
-                                      nullptr);
-  }
-
   const PropertyHandle m_property;
 };