Some more fixes to cros system tray icons (esp. screen tray items)

ash/common/system/tray/tray_item_view.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_COMMON_SYSTEM_TRAY_TRAY_ITEM_VIEW_H_
 #define ASH_COMMON_SYSTEM_TRAY_TRAY_ITEM_VIEW_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 18 matching lines @@
 // animation when showing/hiding the item in the tray.
 class ASH_EXPORT TrayItemView : public views::View,
                                 public gfx::AnimationDelegate {
  public:
   explicit TrayItemView(SystemTrayItem* owner);
   ~TrayItemView() override;
 
   static void DisableAnimationsForTest();
 
   // Convenience function for creating a child Label or ImageView.
+  // Only one of the two should be called.
   void CreateLabel();
   void CreateImageView();
 
   SystemTrayItem* owner() const { return owner_; }
   views::Label* label() const { return label_; }
   views::ImageView* image_view() const { return image_view_; }
 
   // Overridden from views::View.
   void SetVisible(bool visible) override;
   gfx::Size GetPreferredSize() const override;
@@ skipping 11 matching lines @@
   // Overridden from views::View.
   void ChildPreferredSizeChanged(View* child) override;
 
   // Overridden from gfx::AnimationDelegate.
   void AnimationProgressed(const gfx::Animation* animation) override;
   void AnimationEnded(const gfx::Animation* animation) override;
   void AnimationCanceled(const gfx::Animation* animation) override;
 
   SystemTrayItem* owner_;
   std::unique_ptr<gfx::SlideAnimation> animation_;
+  // Only one of |label_| and |image_view_| should be non-null.
   views::Label* label_;
   views::ImageView* image_view_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayItemView);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_ITEM_VIEW_H_