Fixes bug in handling restacking because of transients

ui/aura/mus/window_tree_client.h

Index: ui/aura/mus/window_tree_client.h
diff --git a/ui/aura/mus/window_tree_client.h b/ui/aura/mus/window_tree_client.h
index c43275925da27f33d887c28e3c71a34be8d9b66d..bcbb89705ac406835679f715ca6d3bbfec1cbaf3 100644
--- a/ui/aura/mus/window_tree_client.h
+++ b/ui/aura/mus/window_tree_client.h
@@ -419,6 +419,9 @@ class AURA_EXPORT WindowTreeClient
                                    Window* transient_child) override;
   void OnTransientChildWindowRemoved(Window* parent,
                                      Window* transient_child) override;
+  void OnWillRestackTransientChildAbove(Window* source,
+                                        Window* window) override;
+  void OnDidRestackTransientChildAbove(Window* source, Window* window) override;
 
   // Overriden from DragDropControllerHost:
   uint32_t CreateChangeIdForDrag(WindowMus* window) override;