Implement left property animation on InvalidatableStyleInterpolation

Source/core/animation/InterpolationType.h

Index: Source/core/animation/InterpolationType.h
diff --git a/Source/core/animation/InterpolationType.h b/Source/core/animation/InterpolationType.h
index 1962d8dbce584061fb83655190c75de9044b25cb..a1c98a14633faec390467db0db4e80961e39c8c5 100644
--- a/Source/core/animation/InterpolationType.h
+++ b/Source/core/animation/InterpolationType.h
@@ -31,15 +31,26 @@ public:
     };
     using ConversionCheckers = WillBeHeapVector<OwnPtrWillBeMember<ConversionChecker>>;
 
-    virtual PassOwnPtrWillBeRawPtr<PairwisePrimitiveInterpolation> maybeConvertPairwise(const CSSPropertySpecificKeyframe& startKeyframe, const CSSPropertySpecificKeyframe& endKeyframe, const StyleResolverState*, ConversionCheckers&) const
+    virtual PassOwnPtrWillBeRawPtr<PairwisePrimitiveInterpolation> maybeConvertPairwise(const CSSPropertySpecificKeyframe& startKeyframe, const CSSPropertySpecificKeyframe& endKeyframe, const StyleResolverState* state, ConversionCheckers& conversionCheckers) const
     {
-        return nullptr;
+        OwnPtrWillBeRawPtr<InterpolationValue> startValue = maybeConvertSingle(startKeyframe, state, conversionCheckers);
+        if (!startValue)
+            return nullptr;
+        OwnPtrWillBeRawPtr<InterpolationValue> endValue = maybeConvertSingle(endKeyframe, state, conversionCheckers);
+        if (!endValue)
+            return nullptr;
+        return PairwisePrimitiveInterpolation::create(*this, startValue->m_interpolableValue.release(), endValue->m_interpolableValue.release(), startValue->m_nonInterpolableValue.release());
     }
 
     virtual PassOwnPtrWillBeRawPtr<InterpolationValue> maybeConvertSingle(const CSSPropertySpecificKeyframe&, const StyleResolverState*, ConversionCheckers&) const = 0;
 
+    virtual PassOwnPtrWillBeRawPtr<InterpolationValue> maybeConvertUnderlyingValue(const StyleResolverState&) const = 0;
+
     virtual void apply(const InterpolableValue&, const NonInterpolableValue*, StyleResolverState&) const = 0;
 
+    bool operator==(const InterpolationType& other) const { return this == &other; }
+    bool operator!=(const InterpolationType& other) const { return this != &other; }

[shans, 2015/07/02 12:02:47]

A comment on these would be useful. At first glance they seem almost circular :)
maybe:
// Implement reference equality checking via pointer equality checking as these
are singletons

[alancutter (OOO until 2018), 2015/07/03 01:38:22]

Done.

+
 protected:
     InterpolationType(CSSPropertyID property)
         : m_property(property)