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

ash/system/tray/fixed_sized_image_view.cc

 // 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.
 
 #include "ash/system/tray/fixed_sized_image_view.h"
 
 namespace ash {
 
 FixedSizedImageView::FixedSizedImageView(int width, int height)
     : width_(width),
       height_(height) {
   SetHorizontalAlignment(views::ImageView::CENTER);
   SetVerticalAlignment(views::ImageView::CENTER);
 }
 
 FixedSizedImageView::~FixedSizedImageView() {
 }
 
-gfx::Size FixedSizedImageView::GetPreferredSize() {
+gfx::Size FixedSizedImageView::GetPreferredSize() const {
   gfx::Size size = views::ImageView::GetPreferredSize();
   return gfx::Size(width_ ? width_ : size.width(),
                    height_ ? height_ : size.height());
 }
 
 }  // namespace ash