Add TransitionInterpolation 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..15a180202ca66fedc13003e7851aedb879ca9cfc 100644
--- a/third_party/WebKit/Source/core/animation/InterpolationType.h
+++ b/third_party/WebKit/Source/core/animation/InterpolationType.h
@@ -77,6 +77,16 @@ class InterpolationType {
       const InterpolationValue& underlying,
       ConversionCheckers&) 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 InterpolationValue maybeConvertUnderlyingValue(
       const InterpolationEnvironment&) const = 0;
 
@@ -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;
 };