Make PrefService available in *ash

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 27fdd01267fa128d50b4923a1e829320af92683d..9da78191cd10b0eee6b9f859f0761cad34aefaca 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -364,7 +364,6 @@ class ASH_EXPORT Shell : public SessionObserver,
   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(); }
@@ -422,6 +421,12 @@ class ASH_EXPORT Shell : public SessionObserver,
   // 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();