Aura Shell singleton needs to be destroyed prior to the Aura Desktop

ui/aura_shell/examples/aura_shell_main.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 "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/i18n/icu_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop.h"
 #include "ui/aura/root_window.h"
@@ skipping 105 matching lines @@
   // Create the message-loop here before creating the root window.
   MessageLoop message_loop(MessageLoop::TYPE_UI);
   ui::CompositorTestSupport::Initialize();
 
   aura_shell::Shell::CreateInstance(new ShellDelegateImpl);
 
   aura_shell::examples::InitWindowTypeLauncher();
 
   aura::RootWindow::GetInstance()->Run();
 
+  aura_shell::Shell::DeleteInstance();
+
   aura::RootWindow::DeleteInstance();
 
   ui::CompositorTestSupport::Terminate();
 
   return 0;
 }