Support sandboxed pages in legacy packaged apps

chrome/common/extensions/api/_manifest_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.
 
 {
   "app": {
     "channel": "stable",
     "extension_types": ["packaged_app", "hosted_app", "platform_app"]
   },
   "app.background": {
@@ skipping 177 matching lines @@
   },
   "requirements": {
     "channel": "stable",
     "extension_types": [
       "extension", "packaged_app", "hosted_app", "platform_app"
     ]
   },
   "sandbox": {
     "channel": "stable",
     "extension_types": [
-      "extension", "platform_app"
+      "extension", "platform_app", "packaged_app"
     ],
     "min_manifest_version": 2
   },
   "script_badge": {
     "channel": "dev",
     "extension_types": ["extension"]
   },
   "signature": {
     "channel": "stable",
     "extension_types": "all"
@@ skipping 14 matching lines @@
     "channel": "stable",
     "extension_types": "all"
   },
   "web_accessible_resources": {
     "channel": "stable",
     "extension_types": [
       "extension", "packaged_app", "hosted_app"
     ]
   }
 }