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

ui/views/controls/scrollbar/base_scroll_bar_thumb.h

 // Copyright (c) 2011 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 UI_VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_THUMB_H_
 #define UI_VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_THUMB_H_
 
 #include "ui/gfx/size.h"
 #include "ui/views/controls/button/custom_button.h"
 #include "ui/views/controls/scrollbar/scroll_bar.h"
@@ skipping 26 matching lines @@
   // Retrieves the size (width or height) of the thumb.
   int GetSize() const;
 
   // Sets the position of the thumb on the x or y axis.
   void SetPosition(int position);
 
   // Gets the position of the thumb on the x or y axis.
   int GetPosition() const;
 
   // View overrides:
-  virtual gfx::Size GetPreferredSize() OVERRIDE = 0;
+  virtual gfx::Size GetPreferredSize() const OVERRIDE = 0;
 
  protected:
   // View overrides:
   virtual void OnPaint(gfx::Canvas* canvas) OVERRIDE = 0;
   virtual void OnMouseEntered(const ui::MouseEvent& event) OVERRIDE;
   virtual void OnMouseExited(const ui::MouseEvent& event) OVERRIDE;
   virtual bool OnMousePressed(const ui::MouseEvent& event) OVERRIDE;
   virtual bool OnMouseDragged(const ui::MouseEvent& event) OVERRIDE;
   virtual void OnMouseReleased(const ui::MouseEvent& event) OVERRIDE;
   virtual void OnMouseCaptureLost() OVERRIDE;
@@ skipping 16 matching lines @@
 
   // The current state of the thumb button.
   CustomButton::ButtonState state_;
 
   DISALLOW_COPY_AND_ASSIGN(BaseScrollBarThumb);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_THUMB_H_