Generalize layer mirroring for phantom windows

ui/compositor/layer_owner.cc

 // Copyright (c) 2012 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.
 
 #include "ui/compositor/layer_owner.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "ui/compositor/layer_owner_delegate.h"
@@ skipping 69 matching lines @@
   // Install the delegate last so that the delegate isn't notified as we copy
   // state to the new layer.
   new_layer->set_delegate(old_delegate);
 
   if (layer_owner_delegate_)
     layer_owner_delegate_->OnLayerRecreated(old_layer.get(), new_layer);
 
   return old_layer;
 }
 
+void LayerOwner::MirrorLayer(Layer* mirror) const {
+  DCHECK(OwnsLayer());
+  layer_owner_delegate_->OnLayerMirrored(mirror);
+}
+
 void LayerOwner::DestroyLayer() {
   layer_ = NULL;
   layer_owner_.reset();
 }
 
 bool LayerOwner::OwnsLayer() const {
   return !!layer_owner_;
 }
 
 }  // namespace ui