[Chrome OS MD] Draw a 1px separator between 2 tray items

ash/common/shelf/wm_shelf_observer.h

 // 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.
 
 #ifndef ASH_COMMON_SHELF_WM_SHELF_OBSERVER_H_
 #define ASH_COMMON_SHELF_WM_SHELF_OBSERVER_H_
 
 #include "ash/ash_export.h"
 #include "ash/common/shelf/shelf_types.h"
 #include "ash/common/wm/background_animator.h"
 
 namespace ash {
+class TrayBackgroundView;
 
 // Used to observe changes to the shelf.
 class ASH_EXPORT WmShelfObserver {
  public:
   virtual void OnBackgroundTypeChanged(
       ShelfBackgroundType background_type,
       BackgroundAnimatorChangeType change_type) {}
   virtual void WillChangeVisibilityState(ShelfVisibilityState new_state) {}
   virtual void OnAutoHideStateChanged(ShelfAutoHideState new_state) {}
   virtual void OnShelfIconPositionsChanged() {}
+  virtual void OnVisibilityChange(TrayBackgroundView* tray) {}

[James Cook, 2016/08/09 00:25:17]

nit: Document what this does / when it will be called.

Also, I would name the method something that has "tray" in it, like
OnTrayVisibilityChanging() or similar.  Also, if it's called after the change,
call it "Changed". If before, call it "Changing".

[yiyix, 2016/08/11 01:23:18]

Done.

 
  protected:
   virtual ~WmShelfObserver() {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_WM_SHELF_OBSERVER_H_