@Override
  public void setCurMemStoreOnHeapSizeGauge(long memstoreOnHeapSize) {
    memStoreOnHeapSizeGauge.set(memstoreOnHeapSize);
  }
Hadoop2 implementation of MetricsHeapMemoryManagerSource. Implements BaseSource through
BaseSourceImpl, following the pattern
hbase-hadoop-compat/src/main/java/org/apache/hadoop/hbase/regionserver/MetricsHeapMemoryManagerSourceImpl.java