Add a SigninAllowed policy.

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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 1809 matching lines @@
         'browser/signin/signin_global_error.cc',
         'browser/signin/signin_global_error.h',
         'browser/signin/signin_internals_util.cc',
         'browser/signin/signin_internals_util.h',
         'browser/signin/signin_manager.cc',
         'browser/signin/signin_manager.h',
         'browser/signin/signin_manager_factory.cc',
         'browser/signin/signin_manager_factory.h',
         'browser/signin/signin_names_io_thread.cc',
         'browser/signin/signin_names_io_thread.h',
+        'browser/signin/signin_pref_observer.h',
         'browser/signin/signin_tracker.cc',
         'browser/signin/signin_tracker.h',
         'browser/signin/signin_ui_util.cc',
         'browser/signin/signin_ui_util.h',
         'browser/signin/token_service.cc',
         'browser/signin/token_service.h',
         'browser/signin/token_service_factory.cc',
         'browser/signin/token_service_factory.h',
         'browser/signin/ubertoken_fetcher.cc',
         'browser/signin/ubertoken_fetcher.h',
@@ skipping 1286 matching lines @@
           'variables': {
             'jni_gen_dir': 'chrome',
           },
           'includes': [ '../build/jni_generator.gypi' ],
         },
       ],
      },
     ],
   ],
 }