add 'slow' prefix to RenderObject's firstChild() / lastChild() methods

Source/core/rendering/RenderBoxModelObject.h

Index: Source/core/rendering/RenderBoxModelObject.h
diff --git a/Source/core/rendering/RenderBoxModelObject.h b/Source/core/rendering/RenderBoxModelObject.h
index 30444a54c640bf97846f973b4bef58a8f956aca9..8705cf507d84a0fa926d2069072831e8cd910a0c 100644
--- a/Source/core/rendering/RenderBoxModelObject.h
+++ b/Source/core/rendering/RenderBoxModelObject.h
@@ -294,7 +294,7 @@ public:
     }
     void moveAllChildrenTo(RenderBoxModelObject* toBoxModelObject, RenderObject* beforeChild, bool fullRemoveInsert = false)
     {
-        moveChildrenTo(toBoxModelObject, firstChild(), 0, beforeChild, fullRemoveInsert);
+        moveChildrenTo(toBoxModelObject, slowFirstChild(), 0, beforeChild, fullRemoveInsert);
     }
     // Move all of the kids from |startChild| up to but excluding |endChild|. 0 can be passed as the |endChild| to denote
     // that all the kids from |startChild| onwards should be moved.