@Override
  public void updateBlockedFlushCount(long blockedFlushCount) {
    if (blockedFlushCount > 0) {
      blockedFlushHistogram.add(blockedFlushCount);
      blockedFlushGauge.set(blockedFlushCount);
    }
  }
Hadoop2 implementation of MetricsHeapMemoryManagerSource. Implements BaseSource through
BaseSourceImpl, following the pattern
hbase-hadoop-compat/src/main/java/org/apache/hadoop/hbase/regionserver/MetricsHeapMemoryManagerSourceImpl.java