Whitelist Cast Extension to use WebView.

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 459 matching lines @@
     "channel": "stable",
     "extension_types": ["platform_app"]
   }, {
     "channel": "stable",
     "extension_types": ["extension"],
     "whitelist": [
       "16CA7A47AAE4BE49B1E75A6B960C3875E945B264",  // http://crbug.com/500075
       "F155646B5D1CA545F7E1E4E20D573DFDD44C2540",  // http://crbug.com/500075
       "FA01E0B81978950F2BC5A50512FD769725F57510",  // http://crbug.com/500075
       "B11A93E7E5B541F8010245EBDE2C74647D6C14B9",  // http://crbug.com/500075
-      "63ED55E43214C211F82122ED56407FF1A807F2A3"   // http://crbug.com/500075
+      "63ED55E43214C211F82122ED56407FF1A807F2A3",  // http://crbug.com/500075

[Devlin, 2016/02/18 20:10:56]

Wow.  That's a bunch o' ids.

[apacible, 2016/02/18 21:01:23]

Yeah, once we're done we'll clean up so there will only be two ids left. :)

+      "226CF815E39A363090A1E547D53063472B8279FA"   // http://crbug.com/500075
     ]
   }],
   "webRequest": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
    },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"]
   }
 }