public MetricCollectingService build(HttpService delegate) {
        requireNonNull(delegate, "delegate");
        return new MetricCollectingService(delegate, meterIdPrefixFunction(), successFunction(),
                                           distributionStatisticConfig());
    }
Returns a newly-created {@link MetricCollectingService} decorating {@link HttpService} based
on the properties of this builder.
core/src/main/java/com/linecorp/armeria/server/metric/MetricCollectingServiceBuilder.java