code: void recordDuration( DurationMetric metric,
                           long duration,
                           TimeUnit timeUnit,
                           Map<String, String> payload ) {
          assert metric != null;
          DurationHistory history = durations.get(metric);
          if (history != null) history.recordDuration(duration, timeUnit, payload);
      }
docs: Record a new duration for the given metric, called by the code that knows about the duration.
  
  @param metric the metric; may not be null
  @param duration the duration
  @param timeUnit the time unit of the duration
  @param payload the payload; may be null or a lightweight representation of the activity described by the duration
  @see #increment(ValueMetric)
  @see #increment(ValueMetric, long)
  @see #decrement(ValueMetric)