Add policy provider that would filter extensions/apps allowed on the

extensions/common/features/behavior_feature.cc

 // Copyright 2014 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 "extensions/common/features/behavior_feature.h"
 
 namespace extensions {
 
 const char BehaviorFeature::kWhitelistedForIncognito[] =
     "whitelisted_for_incognito";
 
 const char BehaviorFeature::kDoNotSync[] = "do_not_sync";
 
 const char BehaviorFeature::kZoomWithoutBubble[] = "zoom_without_bubble";
 
+const char BehaviorFeature::kSigninScreen[] = "signin_screen";
+
 }  // namespace extensions