@Override
    public int getSerializedSize(boolean withTags) {
      return super.getSerializedSize(withTags) - this.cell.getValueLength() + this.value.length;
    }
Made into a static method so as to reuse the logic within
ValueAndTagRewriteByteBufferExtendedCell
hbase-common/src/main/java/org/apache/hadoop/hbase/PrivateCellUtil.java