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

Source/core/rendering/RenderLayerScrollableArea.h

Index: Source/core/rendering/RenderLayerScrollableArea.h
diff --git a/Source/core/rendering/RenderLayerScrollableArea.h b/Source/core/rendering/RenderLayerScrollableArea.h
index b3c933ade265141009d2efa4b4d8cf21745c8a39..bf608315d97d9255d1727b9bd4529e587a4efd3d 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.h
+++ b/Source/core/rendering/RenderLayerScrollableArea.h
@@ -249,10 +249,10 @@ private:
     RefPtr<Scrollbar> m_vBar;
 
     // Renderers to hold our custom scroll corner.
-    RenderScrollbarPart* m_scrollCorner;
+    RawPtrWillBePersistent<RenderScrollbarPart> m_scrollCorner;
 
     // Renderers to hold our custom resizer.
-    RenderScrollbarPart* m_resizer;
+    RawPtrWillBePersistent<RenderScrollbarPart> m_resizer;
 };
 
 } // namespace blink