@Override
    public long heapSize() {
      long sum = ClassSize.REFERENCE + super.heapSize();
      if (this.value != null) {
        sum += ClassSize.sizeOf(this.value);
      }
      return sum;
    }
@param cell The original ByteBufferExtendedCell which it rewrites
@param tags the tags bytes. The array suppose to contain the tags bytes alone.
hbase-common/src/main/java/org/apache/hadoop/hbase/PrivateCellUtil.java