Getting rid of SurfaceIdHandler as it is no longer needed.

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 f687f42b04f99e1b550a7262efcdad7edb7369d2..9e7dd27f628030f9ce9f54640c1d7178b9781ef0 100644
--- a/ui/aura/mus/window_port_mus.h
+++ b/ui/aura/mus/window_port_mus.h
@@ -28,7 +28,6 @@ namespace aura {
 
 class ClientSurfaceEmbedder;
 class PropertyConverter;
-class SurfaceIdHandler;
 class Window;
 class WindowPortMusTestApi;
 class WindowTreeClient;
@@ -73,10 +72,6 @@ class AURA_EXPORT WindowPortMus : public WindowPort, public WindowMus {
       std::unique_ptr<WindowCompositorFrameSinkBinding>
           compositor_frame_sink_binding);
 
-  void set_surface_id_handler(SurfaceIdHandler* surface_id_handler) {
-    surface_id_handler_ = surface_id_handler;
-  }
-
  private:
   friend class WindowPortMusTestApi;
   friend class WindowTreeClient;
@@ -250,7 +245,6 @@ class AURA_EXPORT WindowPortMus : public WindowPort, public WindowMus {
   ServerChangeIdType next_server_change_id_ = 0;
   ServerChanges server_changes_;
 
-  SurfaceIdHandler* surface_id_handler_ = nullptr;
   cc::SurfaceInfo surface_info_;
 
   ui::mojom::Cursor predefined_cursor_ = ui::mojom::Cursor::CURSOR_NULL;