[Oilpan] Migrate most classes under core/animations to Oilpan heap.

Source/core/animation/LengthPairStyleInterpolation.cpp

Index: Source/core/animation/LengthPairStyleInterpolation.cpp
diff --git a/Source/core/animation/LengthPairStyleInterpolation.cpp b/Source/core/animation/LengthPairStyleInterpolation.cpp
index 4996158d7cdc8665d889500394e1af2be4222844..f8d8142c38fab9f77fe645c3845a6dfe0ed44fc5 100644
--- a/Source/core/animation/LengthPairStyleInterpolation.cpp
+++ b/Source/core/animation/LengthPairStyleInterpolation.cpp
@@ -16,15 +16,15 @@ bool LengthPairStyleInterpolation::canCreateFrom(const CSSValue& value)
     return value.isPrimitiveValue() && toCSSPrimitiveValue(value).getPairValue();
 }
 
-PassOwnPtrWillBeRawPtr<InterpolableValue> LengthPairStyleInterpolation::lengthPairToInterpolableValue(const CSSValue& value)
+InterpolableValue* LengthPairStyleInterpolation::lengthPairToInterpolableValue(const CSSValue& value)
 {
-    OwnPtrWillBeRawPtr<InterpolableList> result = InterpolableList::create(2);
+    InterpolableList* result = InterpolableList::create(2);
     Pair* pair = toCSSPrimitiveValue(value).getPairValue();
     ASSERT(pair);
 
     result->set(0, LengthStyleInterpolation::toInterpolableValue(*pair->first()));
     result->set(1, LengthStyleInterpolation::toInterpolableValue(*pair->second()));
-    return result.release();
+    return result;
 }
 
 PassRefPtrWillBeRawPtr<CSSValue> LengthPairStyleInterpolation::interpolableValueToLengthPair(InterpolableValue* value, InterpolationRange range)