[Chromoting] Use platformIsMac instead of checking navigator.platform directly.

remoting/webapp/app_remoting/js/loading_window.js

 // 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.
 
 /**
  * @fileoverview
  * Loading dialog for AppRemoting apps.
  */
 
 'use strict';
@@ skipping 25 matching lines @@
 remoting.LoadingWindow.show = function() {
   if (remoting.loadingWindow_) {
     return;
   }
 
   // TODO(garykac): Choose better default timeout.
   // Timeout is currently 15min to handle when we need to spin up a new VM.
   var kConnectionTimeout = 15 * 60 * 1000;
 
   var transparencyWarning = '';
-  if (navigator.platform.indexOf('Mac') != -1) {
+  if (remoting.platformIsMac()) {
     transparencyWarning =
         chrome.i18n.getMessage(/*i18n-content*/'NO_TRANSPARENCY_WARNING');
   }
   remoting.loadingWindow_ = remoting.MessageWindow.showTimedMessageWindow(
       chrome.i18n.getMessage(/*i18n-content*/'PRODUCT_NAME_APP_STREAMING'),
       chrome.i18n.getMessage(/*i18n-content*/'FOOTER_CONNECTING'),
       transparencyWarning,
       chrome.i18n.getMessage(/*i18n-content*/'CANCEL'),
       remoting.MessageWindow.quitApp,
       kConnectionTimeout,
       remoting.LoadingWindow.onTimeout_);
 };
 
 /**
  * Close the loading window.
  */
 remoting.LoadingWindow.close = function() {
   if (remoting.loadingWindow_) {
     remoting.loadingWindow_.close();
   }
   remoting.loadingWindow_ = null;
 };
 
 /** @type {remoting.MessageWindow} */
 remoting.loadingWindow_ = null;