"index" property should be optional with "chrome.tabs.move"

chrome/common/extensions/api/tabs.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": "tabs",
     "dependencies": [ "extension", "windows" ],
     "types": [
       {
@@ skipping 411 matching lines @@
             "name": "tabIds",
             "description": "The tab or list of tabs to move.",
             "choices": [
               {"type": "integer", "minimum": 0},
               {"type": "array", "items": {"type": "integer", "minimum": 0}}
             ]
           },
           {
             "type": "object",
             "name": "moveProperties",
+            "optional": true,
             "properties": {
               "windowId": {
                 "type": "integer",
                 "minimum": -2,
                 "optional": true,
                 "description": "Defaults to the window the tab is currently in."
               },
               "index": {
                 "type": "integer",
                 "minimum": 0,
-                "description": "The position to move the window to. The provided value will be clamped to between zero and the number of tabs in the window."
+                "optional": true,
+                "description": "The position to move the window to. The provided value will be clamped to between zero and the number of tabs in the window. Defaults to the index of the last tab in the window."
               }
             }
           },
           {
             "type": "function",
             "name": "callback",
             "optional": true,
             "parameters": [
               {
                 "name": "tabs",
@@ skipping 391 matching lines @@
             "name": "removeInfo",
             "properties": {
               "isWindowClosing": {"type": "boolean", "description": "True when the tab is being closed because its window is being closed." }
             }
           }
         ]
       }
     ]
   }
 ]