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

ui/aura/mus/client_surface_embedder.h

Index: ui/aura/mus/client_surface_embedder.h
diff --git a/ui/aura/mus/client_surface_embedder.h b/ui/aura/mus/client_surface_embedder.h
index c469789d1bded62da496fd587e033951dff816c7..b8dcc97f13c623abd6b81717d2c8884ccae97b59 100644
--- a/ui/aura/mus/client_surface_embedder.h
+++ b/ui/aura/mus/client_surface_embedder.h
@@ -5,6 +5,8 @@
 #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 {
@@ -62,6 +64,8 @@ class ClientSurfaceEmbedder {
 
   gfx::Insets client_area_insets_;
 
+  scoped_refptr<cc::SurfaceReferenceFactory> ref_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(ClientSurfaceEmbedder);
 };