Add system modals to the proper container in mus+ash.

services/ui/demo/mus_demo_internal.h

 // Copyright 2017 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 SERVICES_UI_DEMO_MUS_DEMO_INTERNAL_H_
 #define SERVICES_UI_DEMO_MUS_DEMO_INTERNAL_H_
 
 #include <map>
 #include <memory>
 #include <set>
@@ skipping 18 matching lines @@
   // ui::demo::MusDemo:
   void OnStartImpl() final;
   std::unique_ptr<aura::WindowTreeClient> CreateWindowTreeClient() final;
 
   // aura::WindowManagerDelegate:
   void SetWindowManagerClient(aura::WindowManagerClient* client) final;
   bool OnWmSetBounds(aura::Window* window, gfx::Rect* bounds) final;
   bool OnWmSetProperty(aura::Window* window,
                        const std::string& name,
                        std::unique_ptr<std::vector<uint8_t>>* new_data) final;
+  void OnWmSetModalType(aura::Window* window, ModalType type) final;
   void OnWmSetCanFocus(aura::Window* window, bool can_focus) final;
   aura::Window* OnWmCreateTopLevelWindow(
       ui::mojom::WindowType window_type,
       std::map<std::string, std::vector<uint8_t>>* properties) final;
   void OnWmClientJankinessChanged(const std::set<aura::Window*>& client_windows,
                                   bool janky) final;
   void OnWmWillCreateDisplay(const display::Display& display) final;
   void OnWmNewDisplay(std::unique_ptr<aura::WindowTreeHostMus> window_tree_host,
                       const display::Display& display) final;
   void OnWmDisplayRemoved(aura::WindowTreeHostMus* window_tree_host) final;
@@ skipping 12 matching lines @@
   bool IsWindowActive(aura::Window* window) final;
   void OnWmDeactivateWindow(aura::Window* window) final;
 
   DISALLOW_COPY_AND_ASSIGN(MusDemoInternal);
 };
 
 }  // namespace demo
 }  // namespace ui
 
 #endif  // SERVICES_UI_DEMO_MUS_DEMO_INTERNAL_H_