Add a SupervisedUserServiceObserver.

chrome/chrome_browser.gypi

 # Copyright 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': {
     # All .cc, .h, .m, and .mm files under browser except for:
     # * tests and mocks.
     # * code below browser/chromeos
     # * code below browser/extensions
@@ skipping 2267 matching lines @@
       'browser/supervised_user/supervised_user_registration_utility.cc',
       'browser/supervised_user/supervised_user_registration_utility.h',
       'browser/supervised_user/supervised_user_registration_utility_stub.cc',
       'browser/supervised_user/supervised_user_registration_utility_stub.h',
       'browser/supervised_user/supervised_user_resource_throttle.cc',
       'browser/supervised_user/supervised_user_resource_throttle.h',
       'browser/supervised_user/supervised_user_service.cc',
       'browser/supervised_user/supervised_user_service.h',
       'browser/supervised_user/supervised_user_service_factory.cc',
       'browser/supervised_user/supervised_user_service_factory.h',
+      'browser/supervised_user/supervised_user_service_observer.h',
       'browser/supervised_user/supervised_user_settings_service.cc',
       'browser/supervised_user/supervised_user_settings_service.h',
       'browser/supervised_user/supervised_user_settings_service_factory.cc',
       'browser/supervised_user/supervised_user_settings_service_factory.h',
       'browser/supervised_user/supervised_user_shared_settings_service.cc',
       'browser/supervised_user/supervised_user_shared_settings_service.h',
       'browser/supervised_user/supervised_user_shared_settings_service_factory.cc',
       'browser/supervised_user/supervised_user_shared_settings_service_factory.h',
       'browser/supervised_user/supervised_user_shared_settings_update.cc',
       'browser/supervised_user/supervised_user_shared_settings_update.h',
@@ skipping 1283 matching lines @@
           'variables': {
             'proto_in_dir': 'browser/sync_file_system/drive_backend',
             'proto_out_dir': 'chrome/browser/sync_file_system/drive_backend',
           },
           'includes': [ '../build/protoc.gypi' ]
         },
       ],
     },],
   ],
 }