Change name of NativeTheme::instance() to make it clear it's web only.

ui/views/controls/menu/menu_config_mac.mm

 // Copyright 2014 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_config.h"
 
 #import <AppKit/AppKit.h>
 
 #include "ui/gfx/image/image_skia.h"
 #include "ui/native_theme/native_theme_mac.h"
 #include "ui/views/controls/menu/menu_image_util.h"
 
 namespace views {
 
 void MenuConfig::Init(const ui::NativeTheme* theme) {
+  DCHECK_EQ(theme, ui::NativeThemeMac::instance());
   font_list = gfx::FontList(gfx::Font([NSFont menuFontOfSize:0.0]));
   menu_vertical_border_size = 4;
   item_top_margin = item_no_icon_top_margin = 1;
   item_bottom_margin = item_no_icon_bottom_margin = 1;
   item_left_margin = 2;
   arrow_to_edge_padding = 12;
   icon_to_label_padding = 4;
   check_width = 19;
   check_height = 11;
   separator_height = 13;
   separator_upper_height = 7;
   separator_lower_height = 6;
   align_arrow_and_shortcut = true;
   icons_in_label = true;
   check_selected_combobox_item = true;
   corner_radius = 5;
   use_outer_border = false;
 }
 
 // static
 const MenuConfig& MenuConfig::instance(const ui::NativeTheme* theme) {
-  CR_DEFINE_STATIC_LOCAL(MenuConfig, mac_instance,
-                         (theme ? theme : ui::NativeTheme::instance()));
+  CR_DEFINE_STATIC_LOCAL(MenuConfig, mac_instance, theme);
   return mac_instance;
 }
 
 }  // namespace views