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

extensions/common/features/behavior_feature.cc

Index: extensions/common/features/behavior_feature.cc
diff --git a/extensions/common/features/behavior_feature.cc b/extensions/common/features/behavior_feature.cc
index 69c2e3653f529329d95211cf8184447801498399..2cc576502a3c5332bc5c159328ea18a3948ec889 100644
--- a/extensions/common/features/behavior_feature.cc
+++ b/extensions/common/features/behavior_feature.cc
@@ -13,4 +13,9 @@ const char BehaviorFeature::kDoNotSync[] = "do_not_sync";
 
 const char BehaviorFeature::kZoomWithoutBubble[] = "zoom_without_bubble";
 
+const char BehaviorFeature::kSigninScreen[] = "signin_screen";
+
+const char BehaviorFeature::kSigninScreenWhitelist[] =
+    "signin_screen_whitelist";
+
 }  // namespace extensions