default void preSplitRegion(final ObserverContext<MasterCoprocessorEnvironment> c,
    final TableName tableName, final byte[] splitRow) throws IOException {
  }
Called before the split region procedure is called.
@param c         the environment to interact with the framework and master
@param tableName the table where the region belongs to
@param splitRow  split point
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MasterObserver.java