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