Remove lock screen item from menu and disable screen lock on guest session.

chrome/browser/ui/toolbar/wrench_menu_model_chromeos.cc

 // Copyright (c) 2011 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.
 
 #include "chrome/browser/ui/toolbar/wrench_menu_model.h"
 
 #include "base/command_line.h"
 #include "base/i18n/number_formatting.h"
 #include "chrome/app/chrome_command_ids.h"
 #include "chrome/browser/task_manager/task_manager.h"
@@ skipping 54 matching lines @@
   SetIcon(GetIndexOfCommandId(IDC_HELP_PAGE),
           *rb.GetBitmapNamed(IDR_HELP_MENU));
 
   // Show IDC_FEEDBACK in top-tier wrench menu for ChromeOS.
   AddItemWithStringId(IDC_FEEDBACK, IDS_FEEDBACK);
 
   AddGlobalErrorMenuItems();
 
   AddSeparator();
 
-  AddItemWithStringId(IDC_LOCK_SCREEN, IDS_LOCK_SCREEN);
-
   if (CommandLine::ForCurrentProcess()->HasSwitch(switches::kGuestSession)) {
     AddItemWithStringId(IDC_EXIT, IDS_EXIT_GUEST_MODE);
   } else {
+    AddItemWithStringId(IDC_LOCK_SCREEN, IDS_LOCK_SCREEN);
     AddItemWithStringId(IDC_EXIT, IDS_SIGN_OUT);
   }
 }