2nd display should show the same background as login/lock screen:

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',
   },
 
@@ skipping 43 matching lines @@
         'accelerators/nested_dispatcher_controller.h',
         'ash_switches.cc',
         'ash_switches.h',
         'caps_lock_delegate.h',
         'desktop_background/desktop_background_controller.cc',
         'desktop_background/desktop_background_controller.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',
         'drag_drop/drag_drop_controller.cc',
         'drag_drop/drag_drop_controller.h',
         'drag_drop/drag_image_view.cc',
         'drag_drop/drag_image_view.h',
         'event_rewriter_delegate.h',
         'focus_cycler.cc',
         'focus_cycler.h',
         'high_contrast/high_contrast_controller.cc',
         'high_contrast/high_contrast_controller.h',
         'launcher/app_list_button.cc',
@@ skipping 528 matching lines @@
             'shell/cocoa/app-Info.plist',
           ],
           'xcode_settings': {
             'INFOPLIST_FILE': 'shell/cocoa/app-Info.plist',
           },
         }],
       ],
     },
   ],
 }