Adding a gray semi transparent backdrop behind the topmost window within the default container

ash/wm/workspace_controller.h

 // 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.
 
 #ifndef ASH_WM_WORKSPACE_CONTROLLER_H_
 #define ASH_WM_WORKSPACE_CONTROLLER_H_
 
 #include "ash/ash_export.h"
 #include "ash/wm/workspace/workspace_types.h"
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace aura {
 class Window;
 }
 
 namespace ash {
 namespace internal {
 
 class ShelfLayoutManager;
 class WorkspaceControllerTestHelper;
 class WorkspaceEventHandler;
 class WorkspaceLayoutManager;
+class MaximizeBackdropDelegate;
 
 // WorkspaceController acts as a central place that ties together all the
 // various workspace pieces.
 class ASH_EXPORT WorkspaceController {
  public:
   explicit WorkspaceController(aura::Window* viewport);
   virtual ~WorkspaceController();
 
   // Returns the current window state.
   WorkspaceWindowState GetWindowState() const;
 
   void SetShelf(ShelfLayoutManager* shelf);
 
   // Starts the animation that occurs on first login.
   void DoInitialAnimation();
 
+  // Add a backdrop behind the top window of the default workspace.
+  void SetMaximizeBackdropDelegate(MaximizeBackdropDelegate* enable);
+
  private:
   friend class WorkspaceControllerTestHelper;
 
   aura::Window* viewport_;
 
   internal::ShelfLayoutManager* shelf_;
   scoped_ptr<internal::WorkspaceEventHandler> event_handler_;
   internal::WorkspaceLayoutManager* layout_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(WorkspaceController);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_WM_WORKSPACE_CONTROLLER_H_