Remove use of index in wallpaper picker code and some refactor

ash/shell.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.h"
 
 #include <algorithm>
 #include <string>
 
 #include "ash/accelerators/focus_manager_factory.h"
 #include "ash/ash_switches.h"
 #include "ash/caps_lock_delegate.h"
 #include "ash/desktop_background/desktop_background_controller.h"
-#include "ash/desktop_background/desktop_background_resources.h"
 #include "ash/desktop_background/desktop_background_view.h"
 #include "ash/desktop_background/user_wallpaper_delegate.h"
 #include "ash/display/display_controller.h"
 #include "ash/display/mouse_cursor_event_filter.h"
 #include "ash/display/display_manager.h"
 #include "ash/display/screen_position_controller.h"
 #include "ash/drag_drop/drag_drop_controller.h"
 #include "ash/focus_cycler.h"
 #include "ash/high_contrast/high_contrast_controller.h"
 #include "ash/magnifier/magnification_controller.h"
@@ skipping 832 matching lines @@
 
 bool Shell::CanAcceptEvents() {
   return true;
 }
 
 ui::EventTarget* Shell::GetParentTarget() {
   return NULL;
 }
 
 }  // namespace ash