[Aura] Support always-on-top top level window.

ui/aura_shell/shell.h

 // 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.
 
 #ifndef UI_AURA_SHELL_SHELL_H_
 #define UI_AURA_SHELL_SHELL_H_
 #pragma once
 
 #include <utility>
 #include <vector>
@@ skipping 12 matching lines @@
 namespace gfx {
 class Rect;
 }
 
 namespace aura_shell {
 
 class Launcher;
 class ShellDelegate;
 
 namespace internal {
+class AlwaysOnTopController;
 class ShelfLayoutController;
 class WorkspaceController;
 }
 
 // Shell is a singleton object that presents the Shell API and implements the
 // Desktop's delegate interface.
 class AURA_SHELL_EXPORT Shell : public aura::DesktopDelegate {
  public:
   // Upon creation, the Shell sets itself as the Desktop's delegate, which takes
   // ownership of the Shell.
@@ skipping 34 matching lines @@
   base::WeakPtrFactory<Shell> method_factory_;
 
   scoped_ptr<ShellDelegate> delegate_;
 
   scoped_ptr<Launcher> launcher_;
 
   scoped_ptr<internal::WorkspaceController> workspace_controller_;
 
   scoped_ptr<internal::ShelfLayoutController> shelf_layout_controller_;
 
+  scoped_ptr<internal::AlwaysOnTopController> always_on_top_controller_;
+
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };
 
 }  // namespace aura_shell
 
 #endif  // UI_AURA_SHELL_SHELL_H_