Convert wallpaper picker to v2 app

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 287 matching lines @@
     "extension_types": [
       "extension", "packaged_app", "hosted_app", "platform_app"
     ]
   },
   "videoCapture": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   },
   "wallpaperPrivate": {
     "channel": "stable",
-    "extension_types": ["extension", "packaged_app"],
+    "extension_types": ["extension", "packaged_app", "platform_app"],
     "location": "component"
   },
   "webNavigation": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app"]
   },
   "webSocketProxyPrivate": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app"],
     "whitelist": [
@@ skipping 14 matching lines @@
   },
   "webRequest": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app"]
   },
   "webRequestBlocking": {
     "channel": "stable",
     "extension_types": ["extension", "packaged_app"]
   }
 }