views: Make view::Views::GetPreferredSize() const.

ash/system/tray/tray_bar_button_with_title.h

 // Copyright 2013 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_TRAY_BAR_BUTTON_WITH_TITLE_H_
 #define ASH_SYSTEM_TRAY_TRAY_BAR_BUTTON_WITH_TITLE_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/views/controls/button/custom_button.h"
@@ skipping 13 matching lines @@
                          int title_id,
                          int width);
   virtual ~TrayBarButtonWithTitle();
 
   void UpdateButton(bool control_on);
 
  private:
   class TrayBarButton;
 
   // Overridden from views::CustomButton:
-  virtual gfx::Size GetPreferredSize() OVERRIDE;
+  virtual gfx::Size GetPreferredSize() const OVERRIDE;
   virtual void Layout() OVERRIDE;
 
   TrayBarButton* image_;
   views::Label* title_;
   int width_;
   int image_height_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayBarButtonWithTitle);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_TRAY_BAR_BUTTON_WITH_TITLE_H_