Aura-Mus: Enable Surface Synchronization behind flag

ui/aura/mus/window_port_mus.h

Index: ui/aura/mus/window_port_mus.h
diff --git a/ui/aura/mus/window_port_mus.h b/ui/aura/mus/window_port_mus.h
index 7b097feaa5fcb375b673e3e34a930cedafa2d419..80996af0117aeb18ff6e008d682eaee804889e7a 100644
--- a/ui/aura/mus/window_port_mus.h
+++ b/ui/aura/mus/window_port_mus.h
@@ -228,6 +228,7 @@ class AURA_EXPORT WindowPortMus : public WindowPort, public WindowMus {
   const cc::LocalSurfaceId& GetOrAllocateLocalSurfaceId(
       const gfx::Size& surface_size) override;
   void SetPrimarySurfaceInfo(const cc::SurfaceInfo& surface_info) override;
+  void SetFallbackSurfaceInfo(const cc::SurfaceInfo& surface_info) override;
   void DestroyFromServer() override;
   void AddTransientChildFromServer(WindowMus* child) override;
   void RemoveTransientChildFromServer(WindowMus* child) override;
@@ -258,7 +259,8 @@ class AURA_EXPORT WindowPortMus : public WindowPort, public WindowMus {
                          int64_t old_value,
                          std::unique_ptr<ui::PropertyData> data) override;
 
-  void UpdatePrimarySurfaceInfoInternal();
+  void UpdatePrimarySurfaceInfo();
+  void UpdateClientSurfaceEmbedder();
 
   WindowTreeClient* window_tree_client_;