Add whitelist for the chrome.syncedNotificationsPrivate API.

Additionally, promotes the API to dev channel since it is appropriately
restricted.

BUG=400436

Review URL: https://codereview.chromium.org/439393003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288109 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/api/_permission_features.json

@@ -965,8 +965,11 @@
     "extension_types": ["platform_app"]
   },
   "syncedNotificationsPrivate": {
-    "channel": "trunk",
-    "extension_types": ["platform_app"]
+    "channel": "dev",
+    "extension_types": ["platform_app"],
+    "whitelist": [
+      "34967F9FA3C399E1EC380B443D7331AA93AC445B"  // http://crbug.com/400436
+    ]
   },
   "system.cpu": {
     "channel": "stable",