Oilpan: Prepare to move RenderObject and RenderObjectChildList to Oilpan heap.

Source/core/rendering/RenderLayerReflectionInfo.h

Index: Source/core/rendering/RenderLayerReflectionInfo.h
diff --git a/Source/core/rendering/RenderLayerReflectionInfo.h b/Source/core/rendering/RenderLayerReflectionInfo.h
index 51198a4482f29df8b33f4721c6fb0d3bb806d69a..4bc655d205f6d6e21447607f8afebde885241a32 100644
--- a/Source/core/rendering/RenderLayerReflectionInfo.h
+++ b/Source/core/rendering/RenderLayerReflectionInfo.h
@@ -72,8 +72,11 @@ public:
     String debugName() const;
 
 private:
-    RenderBox& m_box;
-    RenderReplica* m_reflection;
+    RenderBox& box() { return *m_box; }
+    const RenderBox& box() const { return *m_box; }
+
+    RawPtrWillBePersistent<RenderBox> m_box;
+    RawPtrWillBePersistent<RenderReplica> m_reflection;
 
     // A state bit tracking if we are painting inside a replica.
     unsigned m_isPaintingInsideReflection : 1;