Disable Set wallpaper option in context menu for guest user instead of remove it

ash/shell_context_menu.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 "ash/shell_context_menu.h"
 
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/shell.h"
 #include "grit/ash_strings.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/views/controls/menu/menu_model_adapter.h"
 #include "ui/views/controls/menu/menu_runner.h"
 
 namespace ash {
 namespace internal {
 
 ShellContextMenu::ShellContextMenu() {
 }
 
 ShellContextMenu::~ShellContextMenu() {
 }
 
 void ShellContextMenu::ShowMenu(views::Widget* widget,
                                 const gfx::Point& location) {
-  if (!Shell::GetInstance()->user_wallpaper_delegate()->
-      CanOpenSetWallpaperPage())
-    return;
   ui::SimpleMenuModel menu_model(this);
   menu_model.AddItem(MENU_CHANGE_WALLPAPER,
       l10n_util::GetStringUTF16(IDS_AURA_SET_DESKTOP_WALLPAPER));
   views::MenuModelAdapter menu_model_adapter(&menu_model);
   menu_runner_.reset(new views::MenuRunner(menu_model_adapter.CreateMenu()));
   if (menu_runner_->RunMenuAt(
           widget, NULL, gfx::Rect(location, gfx::Size()),
           views::MenuItemView::TOPRIGHT, views::MenuRunner::HAS_MNEMONICS) ==
       views::MenuRunner::MENU_DELETED)
     return;
 }
 
 bool ShellContextMenu::IsCommandIdChecked(int command_id) const {
   return false;
 }
 
 bool ShellContextMenu::IsCommandIdEnabled(int command_id) const {
-  return true;
+  switch (static_cast<MenuItem>(command_id)) {
+    case MENU_CHANGE_WALLPAPER: {
+      return Shell::GetInstance()->user_wallpaper_delegate()->
+          CanOpenSetWallpaperPage();
+    }
+    default:
+      return true;
+  }
 }
 
 void ShellContextMenu::ExecuteCommand(int command_id) {
   switch (static_cast<MenuItem>(command_id)) {
     case MENU_CHANGE_WALLPAPER: {
       Shell::GetInstance()->user_wallpaper_delegate()->
           OpenSetWallpaperPage();
       break;
     }
   }
 }
 
 bool ShellContextMenu::GetAcceleratorForCommandId(
       int command_id,
       ui::Accelerator* accelerator) {
   return false;
 }
 
 }  // namespace internal
 }  // namespace ash