Generalize layer mirroring for phantom windows

ash/common/wm/forwarding_layer_delegate.h

-// Copyright 2016 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_COMMON_WM_FORWARDING_LAYER_DELEGATE_H_
-#define ASH_COMMON_WM_FORWARDING_LAYER_DELEGATE_H_
-
-#include "base/macros.h"
-#include "base/scoped_observer.h"
-#include "ui/compositor/layer_delegate.h"
-#include "ui/compositor/layer_observer.h"
-
-namespace ui {
-class Layer;
-}
-
-namespace ash {
-
-class WmWindow;
-
-namespace wm {
-
-// A layer delegate to paint the content of a recreated layer by delegating
-// the paint request to the original delegate. It is a delegate of the recreated
-// layer and an observer of the original layer.
-class ForwardingLayerDelegate : public ui::LayerDelegate,
-                                public ui::LayerObserver {
- public:
-  ForwardingLayerDelegate(ui::Layer* new_layer, ui::Layer* original_layer);
-  ~ForwardingLayerDelegate() override;
-
-  // ui:LayerDelegate:
-  void OnPaintLayer(const ui::PaintContext& context) override;
-  void OnDelegatedFrameDamage(const gfx::Rect& damage_rect_in_dip) override;
-  void OnDeviceScaleFactorChanged(float device_scale_factor) override;
-
-  // ui::LayerObserver:
-  void DidPaintLayer(ui::Layer* layer, const gfx::Rect& rect) override;
-  void SurfaceChanged(ui::Layer* layer) override;
-  void LayerDestroyed(ui::Layer* layer) override;
-
- private:
-  // The layer for which |this| is the delegate.
-  ui::Layer* client_layer_;
-
-  // The layer that was recreated to replace |new_layer_|.
-  ui::Layer* original_layer_;
-
-  ScopedObserver<ui::Layer, ui::LayerObserver> scoped_observer_;
-
-  DISALLOW_COPY_AND_ASSIGN(ForwardingLayerDelegate);
-};
-
-}  // namespace wm
-}  // namespace ash
-
-#endif  // ASH_COMMON_WM_FORWARDING_LAYER_DELEGATE_H_