Generalize layer mirroring for phantom windows

ash/common/wm/forwarding_layer_delegate.cc

Index: ash/common/wm/forwarding_layer_delegate.cc
diff --git a/ash/common/wm/forwarding_layer_delegate.cc b/ash/common/wm/forwarding_layer_delegate.cc
index 55a12042f98821d70b9fe1b74e407d9ea8d0d181..0d2f947935cbe59fa5dc848d43b61d7961ddd9ce 100644
--- a/ash/common/wm/forwarding_layer_delegate.cc
+++ b/ash/common/wm/forwarding_layer_delegate.cc
@@ -4,7 +4,6 @@
 
 #include "ash/common/wm/forwarding_layer_delegate.h"
 
-#include "ash/common/wm_window.h"
 #include "base/callback.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_owner.h"
@@ -12,9 +11,9 @@
 namespace ash {
 namespace wm {
 
-ForwardingLayerDelegate::ForwardingLayerDelegate(ui::Layer* new_layer,
+ForwardingLayerDelegate::ForwardingLayerDelegate(ui::Layer* client_layer,
                                                  ui::Layer* original_layer)
-    : client_layer_(new_layer),
+    : client_layer_(client_layer),
       original_layer_(original_layer),
       scoped_observer_(this) {
   scoped_observer_.Add(original_layer);
@@ -45,27 +44,8 @@ void ForwardingLayerDelegate::DidPaintLayer(ui::Layer* layer,
   client_layer_->SchedulePaint(rect);
 }
 
-void ForwardingLayerDelegate::SurfaceChanged(ui::Layer* layer) {
-  // This will delete the old layer and any descendants.
-  ui::LayerOwner old_client;
-  old_client.SetLayer(client_layer_);
-
-  ui::LayerOwner* owner = layer->owner();
-  // The layer recreation step isn't recursive, but layers with surfaces don't
-  // tend to have children anyway. We may end up missing some children, but we
-  // can also reach that state if layers are ever added or removed.
-  // TODO(estade): address this if it ever becomes a practical issue.
-  std::unique_ptr<ui::Layer> recreated = owner->RecreateLayer();
-  client_layer_ = recreated.get();
-  old_client.layer()->parent()->Add(recreated.release());
-  old_client.layer()->parent()->Remove(old_client.layer());
-
-  scoped_observer_.Remove(original_layer_);
-  original_layer_ = owner->layer();
-  scoped_observer_.Add(original_layer_);
-}
-
 void ForwardingLayerDelegate::LayerDestroyed(ui::Layer* layer) {
+  DCHECK_EQ(layer, original_layer_);
   original_layer_ = nullptr;
   scoped_observer_.Remove(layer);
 }