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

extensions/common/api/_behavior_features.json

 // 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.
 
 // This features file defines switches used to control Extension behaviour,
 // typically whitelist configuration.
 // See chrome/common/extensions/api/_features.md to understand this file, as
 // well as feature.h, simple_feature.h, and base_feature_provider.h.
 
 {
@@ skipping 23 matching lines @@
       "B11A93E7E5B541F8010245EBDE2C74647D6C14B9",  // http://crbug.com/505879
       "FA01E0B81978950F2BC5A50512FD769725F57510"   // http://crbug.com/505879
     ]
   },
   "zoom_without_bubble": {
     "channel": "stable",
     "extension_types": "all",
     "whitelist": [
       "CBCC42ABED43A4B58FE3810E62AFFA010EB0349F"   // https://crbug.com/538252
     ]
+  },
+  "signin_screen": {
+    "blacklist": [
+      "9E527CDA9D7C50844E8A5DB964A54A640AE48F98"   // Chrome remote desktop
+    ],
+    "channel": "dev",
+    "extension_types": ["platform_app"],
+    "location": "policy",
+    "min_manifest_version": 2,
+    "platforms": ["chromeos"]
+  },
+  "signin_screen_whitelist": {
+    "dependencies" : ["behavior:signin_screen"],
+    "whitelist": [
+      "E24F1786D842E91E74C27929B0B3715A4689A473",  // Gnubby component extension.
+      "6F9E349A0561C78A0D3F41496FE521C5151C7F71",  // Gnubby app
+      "8EBDF73405D0B84CEABB8C7513C9B9FA9F1DC2CE",  // Genius app (help)
+      "3F50C3A83839D9C76334BCE81CDEC06174F266AF"   // Virtual Keyboard
+    ]
   }
 }