Fix loading success.html at the end of chrome://chrome-signin flow

extensions/common/api/_manifest_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 manifest keys implemented under src/extensions.
 // See chrome/common/extensions/api/_features.md to understand this file, as
 // well as feature.h, simple_feature.h, and feature_provider.h.
 
 {
   "action_handlers": {
@@ skipping 314 matching lines @@
       "extension_types": [
         "extension", "legacy_packaged_app", "hosted_app"
       ]
     },
     {
       "channel": "stable",
       "extension_types": ["platform_app"],
       "location": "component"
     }
   ],
-  "webview": {
-    "channel": "stable",
-    "extension_types": ["platform_app"],
-    "min_manifest_version": 2
-  }
+  "webview": [
+    {
+      "channel": "stable",
+      "extension_types": [ "platform_app" ],
+      "min_manifest_version": 2
+    },
+    {
+      "channel": "stable",
+      "extension_types": [ "extension" ],
+      "whitelist": [
+        // Chrome sign-in extension needs to load web accessibile resources
+        // at the end of the sign-in flow.
+        "D519188F86D9ACCEE0412007B227D9936EB9676B"  // http://crbug.com/709117
+      ]
+    }
+  ]
 }