mash: Avoid shelf crashes on display removal.

ash/mus/root_window_controller.h

 // Copyright 2016 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 ASH_MUS_ROOT_WINDOW_CONTROLLER_H_
 #define ASH_MUS_ROOT_WINDOW_CONTROLLER_H_
 
 #include <memory>
 
 #include "ash/mus/disconnected_app_handler.h"
 #include "ash/public/interfaces/container.mojom.h"
 #include "services/ui/public/cpp/window_observer.h"
 #include "services/ui/public/interfaces/window_manager_constants.mojom.h"
 #include "ui/display/display.h"
+#include "ui/display/display_observer.h"
 
 namespace shell {
 class Connector;
 }
 
 namespace ash {
 
 class AlwaysOnTopController;
 class WorkspaceLayoutManager;
 
@@ skipping 36 matching lines @@
   WorkspaceLayoutManager* workspace_layout_manager() {
     return workspace_layout_manager_;
   }
 
   AlwaysOnTopController* always_on_top_controller() {
     return always_on_top_controller_.get();
   }
 
   WmShelfMus* wm_shelf() { return wm_shelf_.get(); }
 
+  void Shutdown();
+
  private:
   friend class WmTestBase;
   friend class WmTestHelper;
 
   gfx::Rect CalculateDefaultBounds(ui::Window* window) const;
   gfx::Rect GetMaximizedWindowBounds() const;
 
   // Creates the necessary set of layout managers in the shell windows.
   void CreateLayoutManagers();
 
@@ skipping 14 matching lines @@
 
   std::unique_ptr<DisconnectedAppHandler> disconnected_app_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(RootWindowController);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_ROOT_WINDOW_CONTROLLER_H_