Allow webview API in an unblessed extension process

chrome/common/extensions/api/_api_features.json

 // Copyright (c) 2012 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.
 
 // See c/c/e/features/* to understand this file, in particular feature.h,
 // simple_feature.h, and base_feature_provider.h.
 
 {
   "activityLogPrivate": {
     "dependencies": ["permission:activityLogPrivate"],
@@ skipping 596 matching lines @@
     // Any webpage can use the webstore API.
     "matches": ["http://*/*", "https://*/*"]
   },
   "webstorePrivate": {
     "dependencies": ["permission:webstorePrivate"],
     "contexts": ["blessed_extension"]
   },
   "webview": {
     "internal": true,
     "dependencies": ["permission:webview"],
-    "contexts": ["blessed_extension"]
+    "contexts": ["blessed_extension", "unblessed_extension"]
   },
   "windows": {
     "dependencies": ["api:tabs"],
     "contexts": ["blessed_extension"]
   }
 }