Change the platform app manifest structure.

chrome/test/data/extensions/api_test/identity/manifest.json

 {
   "name": "identity api test",
   "manifest_version": 2,
   "version": "1",
-  "platform_app": true,
   "permissions": ["experimental"],
-  "background": {"scripts": ["test.js"]},
+  "app": {
+    "background": {"scripts": ["test.js"]}
+  },
   "oauth2": {
     "client_id": "dummy_client_id",
     "scopes": [ "http://dummy/scope" ]
   }
 }