@Override
  public HFileContext clone() {
    try {
      return (HFileContext) super.clone();
    } catch (CloneNotSupportedException e) {
      throw new AssertionError(); // Won't happen
    }
  }
HeapSize implementation. NOTE : The heap size should be altered when new state variable are
added.
@return heap size of the HFileContext
hbase-common/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileContext.java