Hide Night Light behind a flag

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 319 matching lines @@
     return lock_screen_controller_.get();
   }
   MaximizeModeController* maximize_mode_controller() {
     return maximize_mode_controller_.get();
   }
   MediaController* media_controller() { return media_controller_.get(); }
   MruWindowTracker* mru_window_tracker() { return mru_window_tracker_.get(); }
   NewWindowController* new_window_controller() {
     return new_window_controller_.get();
   }
-  NightLightController* night_light_controller() {
-    return night_light_controller_.get();
-  }
+  NightLightController* night_light_controller();
   SessionController* session_controller() { return session_controller_.get(); }
   ShelfController* shelf_controller() { return shelf_controller_.get(); }
   ShelfModel* shelf_model();
   ShutdownController* shutdown_controller() {
     return shutdown_controller_.get();
   }
   SystemTrayController* system_tray_controller() {
     return system_tray_controller_.get();
   }
   SystemTrayDelegate* system_tray_delegate() {
@@ skipping 473 matching lines @@
   base::ObserverList<ShellObserver> shell_observers_;
 
   scoped_refptr<base::SequencedWorkerPool> blocking_pool_;
 
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELL_H_