Expose the chrome.windows.* API to platform 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.
 
 {
   "appNotifications": {
     "extension_types": ["packaged_app", "hosted_app"]
   },
   "background": {
     "extension_types": [
@@ skipping 123 matching lines @@
     "extension_types": ["platform_app"]
   },
   "storage": {
     "extension_types": ["extension", "packaged_app", "platform_app"]
   },
   "systemPrivate": {
     "extension_types": ["extension", "packaged_app", "platform_app"],
     "location": "component"
   },
   "tabs": {
-    "extension_types": ["extension", "packaged_app"]
+    "extension_types": ["extension", "packaged_app", "platform_app"]
   },
   "terminalPrivate": {
     "extension_types": ["extension", "packaged_app", "platform_app"],
     "whitelist": [
       "pnhechapfaindjhompbnflcldabbghjo",  // HTerm
       "okddffdblfhhnmhodogpojmfkjmhinfp"   // HTerm dev
     ]
   },
   "tts": {
     "extension_types": ["extension", "packaged_app", "platform_app"]
@@ skipping 26 matching lines @@
       "afchcafgojfnemjkcbhfekplkmjaldaa"   // Enterprise Web Store
     ]
   },
   "webRequest": {
     "extension_types": ["extension", "packaged_app"]
   },
   "webRequestBlocking": {
     "extension_types": ["extension", "packaged_app"]
   }
 }