Update references to the extension messaging APIs to point to the "runtime"

chrome/common/extensions/api/webstore_private.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.
 
 [
   {
     "namespace":"webstorePrivate",
     "nodoc": "true",
     "functions": [
       {
@@ skipping 38 matching lines @@
                 "localizedName": {
                   "type": "string",
                   "description": "A string to use instead of the raw value of the 'name' key from manifest.json."
                 }
               }
             }
           },
           {
             "name": "callback",
             "type": "function",
-            "description": "Called when the install process completes. Upon failures, chrome.extension.lastError will be set to 'user_canceled' or 'unknown_error'.",
+            "description": "Called when the install process completes. Upon failures, chrome.runtime.lastError will be set to 'user_canceled' or 'unknown_error'.",
             "optional": "true",
             "parameters": []
           }
         ]
       },
       {
         "name": "beginInstallWithManifest3",
         "description": "Initiates the install process for the given extension.",
         "parameters": [
           {
@@ skipping 160 matching lines @@
                 "type": "string",
                 "enum": ["webgl_allowed", "webgl_blocked"]
               }
             ]
           }
         ]
       }
     ]
   }
 ]