@Override
      public void call(MasterObserver observer) throws IOException {
        observer.postCompletedSplitRegionAction(this, regionInfoA, regionInfoB);
      }
Invoked just after a split
@param regionInfoA the new left-hand daughter region
@param regionInfoB the new right-hand daughter region
@param user        the user
hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterCoprocessorHost.java