Disable background mode for v2 packaged apps.

chrome/common/extensions/api/_permission_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.
 
 {
   "activeTab": {
     "channel": "dev",
     "extension_types": ["extension", "packaged_app"],
     "min_manifest_version": 2
   },
@@ skipping 14 matching lines @@
     "channel": "stable",
     "extension_types": ["packaged_app", "hosted_app"]
   },
   "audioCapture": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   },
   "background": {
     "channel": "stable",
     "extension_types": [
-      "extension", "packaged_app", "hosted_app", "platform_app"
+      "extension", "packaged_app", "hosted_app"
     ]
   },
   "bluetooth": {
     "channel": "dev",
     "extension_types": ["platform_app"]
   },
   "bookmarkManagerPrivate": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app"],
     "location": "component"
@@ skipping 328 matching lines @@
   },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app"]
   },
   "webview": {
     "channel": "dev",
     "extension_types": ["platform_app"]
   }
 }