Reorder the NativeViews attached to a view via kViewHostKey according to the position of the view

ui/aura/window.h

Index: ui/aura/window.h
diff --git a/ui/aura/window.h b/ui/aura/window.h
index e2c0d83bb97f748853635c24c18e93292c24a2fa..cd6fa636bee33076a6ce64ba2a208d94de854f22 100644
--- a/ui/aura/window.h
+++ b/ui/aura/window.h
@@ -175,6 +175,9 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
   // see WindowTest.StackingMadrigal for details.
   void StackChildAbove(Window* child, Window* target);
 
+  // Stacks the specified child of this window at the bottom of the z-order.
+  void StackChildAtBottom(Window* child);
+
   // Stacks |child| below |target|. Does nothing if |child| is already below
   // |target|.
   void StackChildBelow(Window* child, Window* target);