Remove use of index in wallpaper picker code and some refactor

ash/ash.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
     'grit_out_dir': '<(SHARED_INTERMEDIATE_DIR)/chrome',
   },
   'includes': [
@@ skipping 50 matching lines @@
         'ash_constants.cc',
         'ash_constants.h',
         'ash_switches.cc',
         'ash_switches.h',
         'caps_lock_delegate.h',
         'caps_lock_delegate_stub.cc',
         'caps_lock_delegate_stub.h',
         'desktop_background/desktop_background_controller.cc',
         'desktop_background/desktop_background_controller.h',
         'desktop_background/desktop_background_controller_observer.h',
-        'desktop_background/desktop_background_resources.cc',
-        'desktop_background/desktop_background_resources.h',
         'desktop_background/desktop_background_view.cc',
         'desktop_background/desktop_background_view.h',
         'desktop_background/desktop_background_widget_controller.cc',
         'desktop_background/desktop_background_widget_controller.h',
         'desktop_background/user_wallpaper_delegate.h',
         'display/display_change_observer_x11.cc',
         'display/display_change_observer_x11.h',
         'display/display_controller.cc',
         'display/display_controller.h',
         'display/display_error_dialog.cc',
@@ skipping 621 matching lines @@
             'shell/cocoa/app-Info.plist',
           ],
           'xcode_settings': {
             'INFOPLIST_FILE': 'shell/cocoa/app-Info.plist',
           },
         }],
       ],
     },
   ],
 }