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

ui/aura/client/aura_constants.h

Index: ui/aura/client/aura_constants.h
diff --git a/ui/aura/client/aura_constants.h b/ui/aura/client/aura_constants.h
index 32c524fde956038ce686a824e2a518186f706e37..5906a27c2454cb3833a022e043022604ffb5863a 100644
--- a/ui/aura/client/aura_constants.h
+++ b/ui/aura/client/aura_constants.h
@@ -13,6 +13,10 @@ namespace ui {
 class InputMethod;
 }
 
+namespace views {
+class View;
+}
+
 namespace aura {
 namespace client {
 
@@ -38,6 +42,15 @@ AURA_EXPORT extern const WindowProperty<bool>* const kConstrainedWindowKey;
 // attention.
 AURA_EXPORT extern const aura::WindowProperty<bool>* const kDrawAttentionKey;
 
+// A property key to indicate the window's host view. If specified, the host
+// view determines the z-order of the window in its parent widget. The host
+// view must have the same parent widget as the window on which the property
+// is set. The z-order of the window is set to the z-order of the host view in
+// the view tree relative to:
+// - views with layers.
+// - views bound to a window via the kHostViewKey.
+AURA_EXPORT extern const WindowProperty<views::View*>* const kHostViewKey;
+
 // A property key to store the window modality.
 AURA_EXPORT extern const WindowProperty<ui::ModalType>* const kModalKey;