Make PrefService available in *ash

ash/shell.h

 // Copyright (c) 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_SHELL_H_
 #define ASH_SHELL_H_
 
 #include <memory>
 #include <utility>
 #include <vector>
@@ skipping 346 matching lines @@
   void set_link_handler_model_factory(
       LinkHandlerModelFactory* link_handler_model_factory) {
     link_handler_model_factory_ = link_handler_model_factory;
   }
   PowerButtonController* power_button_controller() {
     return power_button_controller_.get();
   }
   LockStateController* lock_state_controller() {
     return lock_state_controller_.get();
   }
-  PrefService* pref_service() { return pref_service_.get(); }
   PaletteDelegate* palette_delegate() { return palette_delegate_.get(); }
   ShellDelegate* shell_delegate() { return shell_delegate_.get(); }
   VideoDetector* video_detector() { return video_detector_.get(); }
   WallpaperController* wallpaper_controller() {
     return wallpaper_controller_.get();
   }
   WallpaperDelegate* wallpaper_delegate() { return wallpaper_delegate_.get(); }
   WindowTreeHostManager* window_tree_host_manager() {
     return window_tree_host_manager_.get();
   }
@@ skipping 37 matching lines @@
   }
 
   ToastManager* toast_manager() { return toast_manager_.get(); }
 
   aura::client::ActivationClient* activation_client();
 
   // Force the shelf to query for it's current visibility state.
   // TODO(jamescook): Move to Shelf.
   void UpdateShelfVisibility();
 
+  // Gets the current active user pref service.
+  // In classic ash, it will be null if there's no active user.
+  // In the case of mash, it can be null if it failed to or hasn't yet
+  // connected to the pref service.
+  PrefService* GetActiveUserPrefService() const;

[sky, 2017/04/26 18:14:00]

Please update this description as to how to detect when to reread this.
Specifically around OnActiveUserSessionChanged.

[afakhry, 2017/04/26 18:36:46]

Done.

+
   // Returns WebNotificationTray on the primary root window.
   WebNotificationTray* GetWebNotificationTray();
 
   // Does the primary display have status area?
   bool HasPrimaryStatusArea();
 
   // Returns the system tray on primary display.
   SystemTray* GetPrimarySystemTray();
 
   static void set_initially_hide_cursor(bool hide) {
@@ skipping 364 matching lines @@
   base::ObserverList<ShellObserver> shell_observers_;
 
   scoped_refptr<base::SequencedWorkerPool> blocking_pool_;
 
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELL_H_