mash: Avoid shelf crashes on display removal.

ash/mus/root_window_controller.cc

 // 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.
 
 #include "ash/mus/root_window_controller.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <map>
@@ skipping 117 matching lines @@
       GetWindowByShellWindowId(MashContainerToAshShellWindowId(container));
   DCHECK(wm_window);
   return wm_window->mus_window();
 }
 
 WmWindowMus* RootWindowController::GetWindowByShellWindowId(int id) {
   return WmWindowMus::AsWmWindowMus(
       WmWindowMus::Get(root_)->GetChildByShellWindowId(id));
 }
 
+void RootWindowController::Shutdown() {
+  wm_shelf_->ShutdownShelfWidget();

[sky, 2016/09/01 23:51:17]

Can this be moved to WmRootWindowController? I think there is a bunch of stuff
in RootWindowController::CloseChildWindows that should likely move to
WmRootWindowController.

+}
+
 gfx::Rect RootWindowController::CalculateDefaultBounds(
     ui::Window* window) const {
   if (window->HasSharedProperty(
           ui::mojom::WindowManager::kInitialBounds_Property)) {
     return window->GetSharedProperty<gfx::Rect>(
         ui::mojom::WindowManager::kInitialBounds_Property);
   }
 
   if (GetWindowShowState(window) == ui::mojom::ShowState::FULLSCREEN) {
     return gfx::Rect(0, 0, root_->bounds().width(), root_->bounds().height());
@@ skipping 43 matching lines @@
   WmWindowMus* panel_container =
       GetWindowByShellWindowId(kShellWindowId_PanelContainer);
   std::unique_ptr<PanelLayoutManager> panel_layout_manager =
       base::MakeUnique<PanelLayoutManager>(panel_container);
   panel_layout_manager->SetShelf(wm_shelf_.get());
   panel_container->SetLayoutManager(std::move(panel_layout_manager));
 }
 
 }  // namespace mus
 }  // namespace ash