Enabling webview in app_shell.

extensions/common/api/_api_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 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.
 //
 // Note that specifying "web_page", "blessed_web_page", or "all" as a context
 // type will require manually updating chrome/renderer/resources/dispatcher.cc.
@@ skipping 49 matching lines @@
     "contexts": ["blessed_extension"]
   },
   // This is not a real API, only here for documentation purposes.
   // See http://crbug.com/275944 for background.
   "extensionTypes": {
     "internal": true,
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"],
     "contexts": ["blessed_extension"]
   },
+  "guestViewInternal": [
+    {
+      "internal": true,
+      "channel": "stable",
+      "contexts": ["blessed_extension"]
+    }, {
+      // Component extensions can use the guestViewInternal API from iframes.
+      "location": "component",
+      "internal": true,
+      "dependencies": ["permission:webview"],
+      "contexts": ["unblessed_extension"]
+    }, {
+      "internal": true,
+      "channel": "trunk",
+      "contexts": ["webui"],
+      "matches": ["chrome://extensions-frame/*", "chrome://extensions/*"]
+    }
+  ],
   "hid": {
     "dependencies": ["permission:hid"],
     "contexts": ["blessed_extension"]
   },
   "power": {
     "dependencies": ["permission:power"],
     "contexts": ["blessed_extension"]
   },
   "runtime": {
     "channel": "stable",
@@ skipping 154 matching lines @@
     "dependencies": ["permission:webview"],
     "contexts": ["blessed_extension"]
   }, {
     // Component extensions can use the webViewInternal API from iframes.
     "location": "component",
     "internal": true,
     "dependencies": ["permission:webview"],
     "contexts": ["unblessed_extension"]
   }]
 }