Add a SigninAllowed policy.

chrome/browser/signin/signin_ui_util.cc

 // Copyright (c) 2013 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.
 
 #include "chrome/browser/signin/signin_ui_util.h"
 
 #include "base/sys_string_conversions.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/signin/signin_global_error.h"
@@ skipping 36 matching lines @@
   }
   return NULL;
 }
 
 string16 GetSigninMenuLabel(Profile* profile) {
   GlobalError* error = signin_ui_util::GetSignedInServiceError(profile);
   if (error)
     return error->MenuItemLabel();
 
   // No errors, so just display the signed in user, if any.
-  ProfileSyncService* service = profile->IsSyncAccessible() ?
-      ProfileSyncServiceFactory::GetForProfile(profile) : NULL;
+  ProfileSyncService* service =
+      profile->IsSyncAccessible() ?

[Andrew T Wilson (Slow), 2013/02/07 10:08:11]

This formatting change is fine, but you might want to revert this file to avoid
churn in the revision log.

[Adrian Kuegel, 2013/02/07 11:09:21]

I should have checked that I reformat it the same way it was before. This was
not an intended change, and I reverted the file.

+          ProfileSyncServiceFactory::GetForProfile(profile) : NULL;
 
   // Even if the user is signed in, don't display the "signed in as..."
   // label if we're still setting up sync.
   if (!service || !service->FirstSetupInProgress()) {
     std::string username;
     SigninManager* signin_manager =
         SigninManagerFactory::GetForProfileIfExists(profile);
     if (signin_manager)
       username = signin_manager->GetAuthenticatedUsername();
     if (!username.empty() && !signin_manager->AuthInProgress()) {
@@ skipping 58 matching lines @@
       if (status_label) {
         status_label->assign(l10n_util::GetStringUTF16(
             IDS_SYNC_ERROR_SIGNING_IN));
       }
       break;
   }
 }
 
 
 }  // namespace signin_ui_util