Implement a means of letting native VR Shell control the HTML UI.

chrome/browser/resources/vr_shell/vr_shell_ui.js

 // Copyright 2016 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.
 
 var vrShellUi = (function() {
   'use strict';
 
   var scene = new ui.Scene();
   var uiElements = [];
 
@@ skipping 94 matching lines @@
       scene.updateElement(element.uiElementId, update);
     }
 
     scene.flush();
   }
 
   function domLoaded() {
     api.domLoaded();
   }
 
+  function command(dict) {
+  }
+
   return {
     initialize: initialize,
+    command: command,
   };
 })();
 
 document.addEventListener('DOMContentLoaded', vrShellUi.initialize);