Make the ChromeOS chromecast system tray integration use a private API.

extensions/common/api/_permission_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 permissions for extension APIs implemented
 // under src/extensions.
 
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 
@@ skipping 141 matching lines @@
       "BD8781D757D830FC2E85470A1B6E8A718B7EE0D9",  // http://crbug.com/407693
       "4AC2B6C63C6480D150DFDA13E4A5956EB1D0DDBB",  // http://crbug.com/407693
       "81986D4F846CEDDDB962643FA501D1780DD441BB",  // http://crbug.com/407693
       "89715614FAA2B4C2853802D70261D2A9D0756FC8"   // http://crbug.com/455986
     ]
   },
   "cast": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"],
     "whitelist": [
+      "9448CAB302F268FB4917D06F70703893DCDA26C4",  // Cast Test Extension
       "63ED55E43214C211F82122ED56407FF1A807F2A3",  // Dev
       "FA01E0B81978950F2BC5A50512FD769725F57510",  // Beta
       "B11A93E7E5B541F8010245EBDE2C74647D6C14B9",  // Canary
       "F155646B5D1CA545F7E1E4E20D573DFDD44C2540",  // Google Cast Beta
       "16CA7A47AAE4BE49B1E75A6B960C3875E945B264",  // Google Cast Stable
       "C17CD9E6868D7B9C67926E0EC612EA25C768418F",  // http://crbug.com/457908
       "EF2AB692559EA97C3BBDEA018A8C45F92457BD4E"   // http://crbug.com/457908
     ]
   },
   "declarativeWebRequest": {
@@ skipping 305 matching lines @@
   }],
   "webRequest": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
    },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   }
 }