Expose enums to extension bindings.

extensions/common/api/runtime.json

 // Copyright 2014 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.
 
 // Note: Many of these functions and events are implemented by hand and should
 // not elicit any code generation from the schema compiler. These items are
 // marked "nocompile."
 [
   {
     "namespace": "runtime",
@@ skipping 44 matching lines @@
             "type": "string",
             "enum": ["arm", "x86-32", "x86-64"],
             "description": "The machine's processor architecture."
           },
           "nacl_arch" : {
             "description": "The native client architecture. This may be different from arch on some platforms.",
             "type": "string",
             "enum": ["arm", "x86-32", "x86-64"]
           }
         }
+      },
+      {
+        "id": "UpdateCheckResult",
+        "type": "string",
+        "enum": ["throttled", "no_update", "update_available"],
+        "description": "Result of the update check."
       }
     ],
     "properties": {
       "lastError": {
         "type": "object",
         "optional": true,
         "description": "This will be defined during an API method callback if there was an error",
         "properties": {
           "message": {
             "optional": true,
@@ skipping 83 matching lines @@
         "name": "requestUpdateCheck",
         "type": "function",
         "description": "Requests an update check for this app/extension.",
         "parameters": [
           {
             "type": "function",
             "name": "callback",
             "parameters": [
               {
                 "name": "status",
-                "type": "string",
-                "enum": ["throttled", "no_update", "update_available"],
-                "description": "Result of the update check."
+                "$ref": "UpdateCheckResult"
               },
               {
                 "name": "details",
                 "type": "object",
                 "optional": true,
                 "properties": {
                   "version": {
                     "type": "string",
                     "description": "The version of the available update."
                   }
@@ skipping 292 matching lines @@
             "type": "string",
             "name": "reason",
             "description": "The reason that the event is being dispatched. 'app_update' is used when the restart is needed because the application is updated to a newer version. 'os_update' is used when the restart is needed because the browser/OS is updated to a newer version. 'periodic' is used when the system runs for more than the permitted uptime set in the enterprise policy.",
             "enum": ["app_update", "os_update", "periodic"]
           }
         ]
       }
     ]
   }
 ]