anchor.diff:    int get _checkSum => _usedData + _deletedKeys;
     bool _isModifiedSince(List oldData, int oldCheckSum) =>
         !identical(_data, oldData) || (_checkSum != oldCheckSum);
  +
  +  int get length;
   }
   
   class _OperatorEqualsAndHashCode {
  
positive.code:   }
  }
  
  abstract class _LinkedHashMapMixin<K, V> implements _HashVMBase {
    int _hashCode(e);
    bool _equals(e1, e2);
    int get _checkSum;
  
negative.code: // Iterates through _data[_offset + _step], _data[_offset + 2*_step], ...
  // and checks for concurrent modification.
  class _CompactIterable<E> extends Iterable<E> {
    final _HashBase _table;
    final List _data;
    final int _len;
    final int _offset;
  