Use a framed window on Mac.

remoting/webapp/app_remoting/js/ar_background.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.
 
 /** @type {AppWindow} */
 var mainWindow = null;
 
 /**
  * The main window cannot delete its context menu entries on close because it
  * is being torn down at that point and doesn't have access to the necessary
@@ skipping 10 matching lines @@
   if (mainWindow) {
     mainWindow.focus();
     return;
   }
 
   var typed_screen = /** @type {{availWidth: number, availHeight: number}} */
       (screen);
 
   var windowAttributes = {
     resizable: false,
-    frame: 'none',
+    frame: remoting.platformIsMac() ? 'chrome' : 'none',
     bounds: {
       width: typed_screen.availWidth,
       height: typed_screen.availHeight
     }
   };
 
   function onClosed() {
     mainWindow = null;
     var ids = Object.keys(contextMenuIds);
     for (var i = 0; i < ids.length; ++i) {
@@ skipping 23 matching lines @@
       contextMenuIds[id] = true;
       break;
     case 'removeContextMenuId':
       delete contextMenuIds[id];
       break;
   }
 };
 
 chrome.app.runtime.onLaunched.addListener(createWindow);
 window.addEventListener('message', onWindowMessage, false);