aura-mus: Implement stacking in DesktopWindowTreeHostMus.

ui/aura/test/mus/test_window_tree.h

 // Copyright 2015 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_TEST_MUS_TEST_WINDOW_TREE_H_
 #define UI_AURA_TEST_MUS_TEST_WINDOW_TREE_H_
 
 #include <stdint.h>
 
 #include <vector>
@@ skipping 159 matching lines @@
                            uint32_t window_id,
                            ui::mojom::Cursor cursor_id) override;
   void SetWindowTextInputState(uint32_t window_id,
                                mojo::TextInputStatePtr state) override;
   void SetImeVisibility(uint32_t window_id,
                         bool visible,
                         mojo::TextInputStatePtr state) override;
   void OnWindowInputEventAck(uint32_t event_id,
                              ui::mojom::EventResult result) override;
   void DeactivateWindow(uint32_t window_id) override;
+  void StackAtTop(uint32_t change_id, uint32_t window_id) override;
   void GetWindowManagerClient(
       mojo::AssociatedInterfaceRequest<ui::mojom::WindowManagerClient> internal)
       override;
   void GetCursorLocationMemory(
       const GetCursorLocationMemoryCallback& callback) override;
   void PerformDragDrop(
       uint32_t change_id,
       uint32_t source_window_id,
       const std::unordered_map<std::string, std::vector<uint8_t>>& drag_data,
       uint32_t drag_operation) override;
@@ skipping 25 matching lines @@
   gfx::Insets last_client_area_;
 
   base::Optional<gfx::Rect> last_hit_test_mask_;
 
   DISALLOW_COPY_AND_ASSIGN(TestWindowTree);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_TEST_MUS_TEST_WINDOW_TREE_H_