@Override
  public String getJsonString() {
    JsonObject json = (JsonObject) GSON.toJsonTree(this);
    json.add("largestCellParts", buildLargestCellPartsJson());
    json.addProperty("largestRowAsString", getLargestRowAsString());
    json.add("rowSizeBuckets", rowSizeBuckets.toJsonObject());
    json.add("valueSizeBuckets", valueSizeBuckets.toJsonObject());
    return json.toString();
  }
Clone the cell refs so they can be cleaned up by {@link Shipper#shipped()}. Doing this lazily
here, rather than eagerly in the above two methods can save us on some allocations. We might
change the largestCell/largestRow multiple times between shipped() calls.
hbase-examples/src/main/java/org/apache/hadoop/hbase/coprocessor/example/row/stats/RowStatisticsImpl.java