@Override
  public void updateBlockCacheDeltaSizeHistogram(int blockCacheDeltaSize) {
    if (blockCacheDeltaSize >= 0) {
      incBlockCacheSizeHistogram.add(blockCacheDeltaSize);
    } else if (blockCacheDeltaSize < 0) {
      decBlockCacheSizeHistogram.add(-blockCacheDeltaSize);
    }
  }
Hadoop2 implementation of MetricsHeapMemoryManagerSource. Implements BaseSource through
BaseSourceImpl, following the pattern
hbase-hadoop-compat/src/main/java/org/apache/hadoop/hbase/regionserver/MetricsHeapMemoryManagerSourceImpl.java