aura-mus: Implement stacking in DesktopWindowTreeHostMus.

ui/aura/mus/window_tree_client.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_AURA_MUS_WINDOW_TREE_CLIENT_H_
 #define UI_AURA_MUS_WINDOW_TREE_CLIENT_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 412 matching lines @@
                                         const gfx::Rect& bounds) override;
   void OnWindowTreeHostClientAreaWillChange(
       WindowTreeHostMus* window_tree_host,
       const gfx::Insets& client_area,
       const std::vector<gfx::Rect>& additional_client_areas) override;
   void OnWindowTreeHostHitTestMaskWillChange(
       WindowTreeHostMus* window_tree_host,
       const base::Optional<gfx::Rect>& mask_rect) override;
   void OnWindowTreeHostDeactivateWindow(
       WindowTreeHostMus* window_tree_host) override;
+  void OnWindowTreeHostStackAtTop(WindowTreeHostMus* window_tree_host) override;
   std::unique_ptr<WindowPortMus> CreateWindowPortForTopLevel(
       const std::map<std::string, std::vector<uint8_t>>* properties) override;
   void OnWindowTreeHostCreated(WindowTreeHostMus* window_tree_host) override;
 
   // Override from client::TransientWindowClientObserver:
   void OnTransientChildWindowAdded(Window* parent,
                                    Window* transient_child) override;
   void OnTransientChildWindowRemoved(Window* parent,
                                      Window* transient_child) override;
   void OnWillRestackTransientChildAbove(Window* parent,
@@ skipping 81 matching lines @@
   std::unique_ptr<DragDropControllerMus> drag_drop_controller_;
 
   base::WeakPtrFactory<WindowTreeClient> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClient);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_CLIENT_H_