Moved FolderImageSource class to a separate file.

ui/app_list/app_list.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,
   },
   'targets': [
     {
@@ skipping 56 matching lines @@
         'cocoa/apps_search_box_controller.h',
         'cocoa/apps_search_box_controller.mm',
         'cocoa/apps_search_results_controller.h',
         'cocoa/apps_search_results_controller.mm',
         'cocoa/apps_search_results_model_bridge.h',
         'cocoa/apps_search_results_model_bridge.mm',
         'cocoa/item_drag_controller.h',
         'cocoa/item_drag_controller.mm',
         'cocoa/scroll_view_with_no_scrollbars.h',
         'cocoa/scroll_view_with_no_scrollbars.mm',
+        'folder_image_source.cc',
+        'folder_image_source.h',
         'pagination_controller.cc',
         'pagination_controller.h',
         'pagination_model.cc',
         'pagination_model.h',
         'pagination_model_observer.h',
         'search_box_model.cc',
         'search_box_model.h',
         'search_box_model_observer.h',
         'search_controller.cc',
         'search_controller.h',
@@ skipping 259 matching lines @@
                 '../../sandbox/sandbox.gyp:sandbox',
                 '../../content/content.gyp:content_startup_helper_win',
               ],
             }],
           ],
         },
       ],
     }],  # toolkit_views==1
   ],
 }