Aura-Mus: Avoid creating StubSurfaceReferenceFactory's on every surface ID change

ui/aura/mus/client_surface_embedder.h

 // Copyright 2017 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 <memory>
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "cc/surfaces/surface_reference_factory.h"
 #include "ui/gfx/geometry/insets.h"
 
 namespace cc {
 class SurfaceInfo;
 }
 
 namespace gfx {
 class Insets;
 }
 
@@ skipping 37 matching lines @@
 
   // Contains the client's content.
   std::unique_ptr<ui::Layer> surface_layer_;
 
   // Used for showing a gutter when the content is not available.
   std::unique_ptr<ui::Layer> right_gutter_;
   std::unique_ptr<ui::Layer> bottom_gutter_;
 
   gfx::Insets client_area_insets_;
 
+  scoped_refptr<cc::SurfaceReferenceFactory> ref_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(ClientSurfaceEmbedder);
 };
 
 }  // namespace aura