Generalize layer mirroring for phantom windows

ash/common/wm/forwarding_layer_delegate.h

Index: ash/common/wm/forwarding_layer_delegate.h
diff --git a/ash/common/wm/forwarding_layer_delegate.h b/ash/common/wm/forwarding_layer_delegate.h
index 446db9c747a7f508b2896232ad3e5e8cb59b789e..4111a4073360caeeec37d23109519d6beb9c6827 100644
--- a/ash/common/wm/forwarding_layer_delegate.h
+++ b/ash/common/wm/forwarding_layer_delegate.h
@@ -15,9 +15,6 @@ class Layer;
 }
 
 namespace ash {
-
-class WmWindow;
-
 namespace wm {
 
 // A layer delegate to paint the content of a recreated layer by delegating
@@ -26,7 +23,7 @@ namespace wm {
 class ForwardingLayerDelegate : public ui::LayerDelegate,
                                 public ui::LayerObserver {
  public:
-  ForwardingLayerDelegate(ui::Layer* new_layer, ui::Layer* original_layer);
+  ForwardingLayerDelegate(ui::Layer* client_layer, ui::Layer* original_layer);
   ~ForwardingLayerDelegate() override;
 
   // ui:LayerDelegate:
@@ -37,14 +34,13 @@ class ForwardingLayerDelegate : public ui::LayerDelegate,
 
   // 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_|.
+  // The layer that was recreated to replace |client_layer_|.
   ui::Layer* original_layer_;
 
   ScopedObserver<ui::Layer, ui::LayerObserver> scoped_observer_;