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

ui/views/controls/menu/menu_separator_win.cc

 // 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.
 
 #include "ui/views/controls/menu/menu_separator.h"
 
 #include <windows.h>
 #include <uxtheme.h>
 #include <Vssym32.h>
 
@@ skipping 29 matching lines @@
   }
 
   gfx::Rect separator_bounds(start_x, 0, width(), height());
   ui::NativeTheme::ExtraParams extra;
   extra.menu_separator.has_gutter = config.render_gutter;
   config.native_theme->Paint(
       canvas->sk_canvas(), ui::NativeTheme::kMenuPopupSeparator,
       ui::NativeTheme::kNormal, separator_bounds, extra);
 }
 
-gfx::Size MenuSeparator::GetPreferredSize() {
+gfx::Size MenuSeparator::GetPreferredSize() const {
   const MenuConfig& config = parent_menu_item_->GetMenuConfig();
 
   if (config.native_theme == ui::NativeThemeAura::instance())
     return GetPreferredSizeAura();
 
   return gfx::Size(10,  // Just in case we're the only item in a menu.
                    config.separator_height);
 }
 
 }  // namespace views