public static Histogram newHistogram(Reservoir sample) {
    try {
      Constructor<?> ctor = Histogram.class.getDeclaredConstructor(Reservoir.class);
      ctor.setAccessible(true);
      return (Histogram) ctor.newInstance(sample);
    } catch (Exception e) {
      throw new RuntimeException(e);
    }
  }
Create a new {@link com.codahale.metrics.Histogram} instance. These constructors are not public
in 2.2.0, so we use reflection to find them.
hbase-server/src/main/java/org/apache/hadoop/hbase/util/YammerHistogramUtils.java