Enabling webview in app_shell.

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 276 matching lines @@
     {
       "channel": "stable",
       "extension_types": ["extension"],
       "whitelist": [
         // http://crbug.com/292856
         "3F50C3A83839D9C76334BCE81CDEC06174F266AF",
         "09FDCB5851B8F3378DB630D06E316076E89C95A6",
         "A434B90223C3C52F2B69DB494736B63C612C774D"
       ]
     }
+  ],
+  "webview": [
+    {
+      "channel": "stable",
+      "extension_types": ["platform_app"]
+    },
+    {
+      // General support for webview in component extensions still in progress.
+      // Only allowed for whitelisted extensions until all the caveats are
+      // addressed. Tracked in crbug/285151.
+      "channel": "stable",
+      "extension_types": ["extension"],
+      "location": "component",
+      "whitelist": [
+        "D519188F86D9ACCEE0412007B227D9936EB9676B"  // GAIA Component Extension
+      ]
+    }
   ]
 }