ash: Reorder shutdown of ShelfLayoutManager and StatusAreaWidget

ash/shelf/shelf_layout_manager.h

 // Copyright 2012 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_SHELF_SHELF_LAYOUT_MANAGER_H_
 #define ASH_SHELF_SHELF_LAYOUT_MANAGER_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 317 matching lines @@
 
   // The RootWindow is cached so that we don't invoke Shell::GetInstance() from
   // our destructor. We avoid that as at the time we're deleted Shell is being
   // deleted too.
   aura::Window* root_window_;
 
   // True when inside UpdateBoundsAndOpacity() method. Used to prevent calling
   // UpdateBoundsAndOpacity() again from SetChildBounds().
   bool updating_bounds_;
 
+  bool in_shutdown_ = false;
+
   // Current state.
   State state_;
 
   ShelfWidget* shelf_;
 
   WorkspaceController* workspace_controller_;
 
   // Do any windows overlap the shelf? This is maintained by WorkspaceManager.
   bool window_overlaps_shelf_;
 
@@ skipping 53 matching lines @@
 
   std::unique_ptr<RootWindowControllerObserverImpl>
       root_window_controller_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfLayoutManager);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_LAYOUT_MANAGER_H_