@Override
    public String toString() {
      return "hfs=" + hfs + ", path=" + pathName + ", fileContext=" + fileContext;
    }
Generates the checksum for the header as well as the data and then validates it. If the block
doesn't uses checksum, returns false.
@return True if checksum matches, else false.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java