Add a SigninAllowed policy.

chrome/browser/profiles/profile.cc

 // 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.
 
 #include "chrome/browser/profiles/profile.h"
 
 #include <string>
 
 #include "build/build_config.h"
 #include "chrome/browser/prefs/pref_service.h"
@@ skipping 111 matching lines @@
 bool Profile::IsGuestSession() const {
 #if defined(OS_CHROMEOS)
   static bool is_guest_session =
       CommandLine::ForCurrentProcess()->HasSwitch(switches::kGuestSession);
   return is_guest_session;
 #else
   return false;
 #endif
 }
 
+bool Profile::IsSigninAllowed() {
+  return GetPrefs()->GetBoolean(prefs::kSigninAllowed);
+}
+
 bool Profile::IsSyncAccessible() {
   browser_sync::SyncPrefs prefs(GetPrefs());
   return ProfileSyncService::IsSyncEnabled() && !prefs.IsManaged();
 }
 
 void Profile::MaybeSendDestroyedNotification() {
   if (!sent_destroyed_notification_) {
     sent_destroyed_notification_ = true;
     content::NotificationService::current()->Notify(
         chrome::NOTIFICATION_PROFILE_DESTROYED,
         content::Source<Profile>(this),
         content::NotificationService::NoDetails());
   }
 }