Speed up custom wallpaper switching time and wallpaper manager code refactor

chrome/chrome_browser.gypi

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
@@ skipping 758 matching lines @@
         'browser/chromeos/login/user_image_screen.cc',
         'browser/chromeos/login/user_image_screen.h',
         'browser/chromeos/login/user_image_screen_actor.h',
         'browser/chromeos/login/user_manager.cc',
         'browser/chromeos/login/user_manager.h',
         'browser/chromeos/login/user_manager_impl.cc',
         'browser/chromeos/login/user_manager_impl.h',
         'browser/chromeos/login/version_info_updater.cc',
         'browser/chromeos/login/version_info_updater.h',
         'browser/chromeos/login/view_screen.h',
+        'browser/chromeos/login/wallpaper_loader.cc',
+        'browser/chromeos/login/wallpaper_loader.h',
         'browser/chromeos/login/wallpaper_manager.cc',
         'browser/chromeos/login/wallpaper_manager.h',
         'browser/chromeos/login/web_page_screen.cc',
         'browser/chromeos/login/web_page_screen.h',
         'browser/chromeos/login/web_page_view.cc',
         'browser/chromeos/login/web_page_view.h',
         'browser/chromeos/login/webui_login_display.cc',
         'browser/chromeos/login/webui_login_display.h',
         'browser/chromeos/login/webui_login_display_host.cc',
         'browser/chromeos/login/webui_login_display_host.h',
@@ skipping 4695 matching lines @@
           'variables': {
             'jni_gen_dir': 'chrome',
           },
           'includes': [ '../build/jni_generator.gypi' ],
         },
       ],
      },
     ],
   ],
 }