Revert of Refactor backdrop

ash/wm/workspace/workspace_layout_manager_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 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 {
+ public:
+  virtual ~WorkspaceLayoutManagerBackdropDelegate() {}
+
+  // 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;
+};
+
+}  // namespace ash
+
+#endif  // ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_BACKDROP_DELEGATE_H_