Refactor backdrop that is currently used in the maximized mode.

ash/wm/workspace/backdrop_delegate.h

 // Copyright 2014 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_WORKSPACE_LAYOUT_MANAGER_BACKDROP_DELEGATE_H_
 #define ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_BACKDROP_DELEGATE_H_
 
 #include "ash/ash_export.h"
-#include "ash/wm/wm_types.h"
+
+namespace aura {
+class Window;
+}
 
 namespace ash {
 
-class WmWindow;
-
-namespace wm {
-class WindowState;
-}
-
 // A delegate which can be set to create and control a backdrop which gets
 // placed below the top level window.
-class ASH_EXPORT WorkspaceLayoutManagerBackdropDelegate {
+class ASH_EXPORT BackdropDelegate {
  public:
-  virtual ~WorkspaceLayoutManagerBackdropDelegate() {}
+  virtual ~BackdropDelegate() {}
 
   // A window got added to the layout.
-  virtual void OnWindowAddedToLayout(WmWindow* child) = 0;
-
-  // A window got removed from the layout.
-  virtual void OnWindowRemovedFromLayout(WmWindow* child) = 0;
-
-  // The visibility of a window has changed.
-  virtual void OnChildWindowVisibilityChanged(WmWindow* child,
-                                              bool visible) = 0;
-
-  // The stacking order of a window has changed.
-  virtual void OnWindowStackingChanged(WmWindow* window) = 0;
-
-  // A window state type has changed.
-  virtual void OnPostWindowStateTypeChange(wm::WindowState* window_state,
-                                           wm::WindowStateType old_type) = 0;
+  virtual bool HasBackdrop(aura::Window* window) = 0;
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_BACKDROP_DELEGATE_H_