Refactor backdrop that is currently used in the maximized mode.

ash/wm/maximize_mode/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_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_
-#define ASH_WM_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_
-
-#include <memory>
-
-#include "ash/ash_export.h"
-#include "ash/wm/workspace/workspace_layout_manager_backdrop_delegate.h"
-#include "base/macros.h"
-
-namespace views {
-class Widget;
-}
-
-namespace ash {
-
-class WmWindow;
-
-// A background which gets created for a container |window| and which gets
-// stacked behind the topmost window (within that container) covering the
-// entire container.
-class ASH_EXPORT WorkspaceBackdropDelegate
-    : public WorkspaceLayoutManagerBackdropDelegate {
- public:
-  explicit WorkspaceBackdropDelegate(WmWindow* container);
-  ~WorkspaceBackdropDelegate() override;
-
-  // WorkspaceLayoutManagerBackdropDelegate overrides:
-  void OnWindowAddedToLayout(WmWindow* child) override;
-  void OnWindowRemovedFromLayout(WmWindow* child) override;
-  void OnChildWindowVisibilityChanged(WmWindow* child, bool visible) override;
-  void OnWindowStackingChanged(WmWindow* window) override;
-  void OnPostWindowStateTypeChange(wm::WindowState* window_state,
-                                   wm::WindowStateType old_type) override;
-
- private:
-  // Restack the backdrop relatively to the other windows in the container.
-  void RestackBackdrop();
-
-  // Returns the current visible top level window in the container.
-  WmWindow* GetCurrentTopWindow();
-
-  // Show the overlay.
-  void Show();
-
-  // The background which covers the rest of the screen.
-  views::Widget* background_ = nullptr;
-  // WmWindow for |background_|.
-  WmWindow* background_window_ = nullptr;
-
-  // The window which is being "maximized".
-  WmWindow* container_;
-
-  // If true, the |RestackOrHideWindow| might recurse.
-  bool in_restacking_;
-
-  DISALLOW_COPY_AND_ASSIGN(WorkspaceBackdropDelegate);
-};
-
-}  // namespace ash
-
-#endif  // ASH_WM_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_