public static Function<? super HttpService, ObservationService>
    newDecorator(ObservationRegistry observationRegistry) {
        requireNonNull(observationRegistry, "observationRegistry");
        return service -> new ObservationService(service, observationRegistry, null);
    }
Creates a new micrometer observation integrated {@link HttpService} decorator using the
specified {@link ObservationRegistry} instance.
core/src/main/java/com/linecorp/armeria/server/observation/ObservationService.java