code: public List<Long> getExtraDataFields() {
          if (mExtraDataFields.getClass().isInstance(UNMODIFIABLE_LIST_OF_LONG)) {
              return mExtraDataFields;
          }
          else {
              return Collections.unmodifiableList(mExtraDataFields);
          }
      }
docs: Returns the list of data fields transmitted with the advertisement
  @return dataFields