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 ec0b4c54fe162a68797baa6a522e904c6b7d99dd..687ce7b8fa1436bcbed67e873fa7dbb0d46c9024 100644
--- a/extensions/common/features/behavior_feature.cc
+++ b/extensions/common/features/behavior_feature.cc
@@ -16,4 +16,6 @@ const char BehaviorFeature::kZoomWithoutBubble[] = "zoom_without_bubble";
 const char BehaviorFeature::kAllowUsbDevicesPermissionInterfaceClass[] =
     "allow_usb_devices_permission_interface_class";
 
+const char BehaviorFeature::kSigninScreen[] = "signin_screen";
+
 }  // namespace extensions