Adds syncedNotificationsPrivate API IDL.

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.
 
 // This features file defines permissions for extension APIs implemented
 // under src/chrome.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 
 // To add a new whitelisted ID, SHA-1 it and force it to uppercase. In Bash:
@@ skipping 808 matching lines @@
       "5D3851BEFF680AB6D954B76678EFCCE834465C23",  // QuickOffice Dev
       "12E618C3C6E97495AAECF2AC12DEB082353241C6",  // QO component extension
       "3727DD3E564B6055387425027AD74C58784ACC15",  // Editor
       "CBCC42ABED43A4B58FE3810E62AFFA010EB0349F"   // PDF
     ]
   },
   "syncFileSystem": {
     "channel": "stable",
     "extension_types": ["platform_app"]
   },
+  "syncedNotificationsPrivate": {
+    "channel": "trunk",
+    "extension_types": ["platform_app"]
+  },
   "system.cpu": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"]
   },
   "system.memory": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"]
   },
   "system.network": {
     "channel": "stable",
@@ skipping 144 matching lines @@
     // Only allowed for whitelisted extensions until all the caveats are
     // addressed. Tracked in crbug/285151.
     "channel": "stable",
     "extension_types": ["extension"],
     "location": "component",
     "whitelist": [
       "D519188F86D9ACCEE0412007B227D9936EB9676B"  // GAIA Component Extension
     ]
   }]
 }