public long addToResponseProcessingTime(long delta) {
      return responseProcessingTimeInMs.addAndGet(delta);
    }
Adds to the time taken to process the response at the NIO layer.
@param delta the time taken in ms to do the current piece of processing at the NIO layer for the response.
@return the total time taken in ms to process the response at the NIO layer, including the current piece, at this
         moment.
ambry-api/src/main/java/com/github/ambry/rest/RestRequestMetricsTracker.java