ash: Animate changes in the uber tray.

ash/system/tray/system_tray_item.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_SYSTEM_TRAY_SYSTEM_TRAY_ITEM_H_
 #define ASH_SYSTEM_TRAY_SYSTEM_TRAY_ITEM_H_
 #pragma once
 
 #include "ash/ash_export.h"
 #include "ash/system/user/login_status.h"
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace views {
 class View;
 }
 
 namespace ash {
 
 class ASH_EXPORT SystemTrayItem {
  public:
   SystemTrayItem();
   virtual ~SystemTrayItem();
 
   // Returns a view to be displayed in the system tray. If this returns NULL,
   // then this item is not displayed in the tray.
+  // NOTE: The returned view should almost always be a TrayItemView, which
+  // automatically resizes the widget when the size of the view changes, and
+  // adds animation when the visibility of the view changes. If a view wants to
+  // avoid these behaviour, then it should not be a TrayItemView.
   virtual views::View* CreateTrayView(user::LoginStatus status) = 0;
 
   // Returns a view for the item to be displayed in the list. This view can be
   // displayed with a number of other tray items, so this should not be too
   // big.
   virtual views::View* CreateDefaultView(user::LoginStatus status) = 0;
 
   // Returns a detailed view for the item. This view is displayed standalone.
   virtual views::View* CreateDetailedView(user::LoginStatus status) = 0;
 
@@ skipping 16 matching lines @@
   void SetDetailedViewCloseDelay(int for_seconds);
 
  private:
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_SYSTEM_TRAY_ITEM_H_