Add a 'hidden' option to chrome.app.window.create()

chrome/common/extensions/api/app_current_window_internal.idl

 // 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.
 
+// This is used by the app window API internally to pass through messages to
+// the shell window.
 [internal, nodoc] namespace app.currentWindowInternal {
   interface Functions {
-    // Focus the window.
     static void focus();
-
-    // Minimize the window.
     static void minimize();
-
-    // Maximize the window.
     static void maximize();
-
-    // Restore the window.
     static void restore();
+    static void show();
+    static void hide();
   };
 };