Generalize layer mirroring for phantom windows

ui/compositor/layer_owner.h

 // 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.
 
 #ifndef UI_COMPOSITOR_LAYER_OWNER_H_
 #define UI_COMPOSITOR_LAYER_OWNER_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
@@ skipping 19 matching lines @@
   // end of ~LayerOwner().
   std::unique_ptr<Layer> AcquireLayer();
 
   // Asks the owner to recreate the layer, returning the old Layer. NULL is
   // returned if there is no existing layer, or recreate is not supported.
   //
   // This does not recurse. Existing children of the layer are moved to the new
   // layer.
   virtual std::unique_ptr<Layer> RecreateLayer();
 
+  // Requests a |mirror| of the owned layer from the LayerOwnerDelegate.

[oshima, 2016/10/04 21:06:31]

how about "Requests to mirror the content of owning layer onto |mirror| layer"?

[Dominik Laskowski, 2016/10/04 23:18:52]

Done.

+  void MirrorLayer(Layer* mirror) const;
+
   ui::Layer* layer() { return layer_; }
   const ui::Layer* layer() const { return layer_; }
 
   void set_layer_owner_delegate(LayerOwnerDelegate* delegate) {
     layer_owner_delegate_ = delegate;
   }
 
  protected:
   void DestroyLayer();
 
   bool OwnsLayer() const;
 
  private:
   // The LayerOwner owns its layer unless ownership is relinquished via a call
   // to AcquireLayer(). After that moment |layer_| will still be valid but
   // |layer_owner_| will be NULL. The reason for releasing ownership is that
   // the client may wish to animate the layer beyond the lifetime of the owner,
   // e.g. fading it out when it is destroyed.
   std::unique_ptr<Layer> layer_owner_;
   Layer* layer_;
 
   LayerOwnerDelegate* layer_owner_delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerOwner);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_LAYER_OWNER_H_