anchor.diff:    }
   }
   
  -class _NodeOperations implements NodeOperations<Expression> {
  -  @override
  -  Expression unwrapParenthesized(Expression node) {
  -    return node.unParenthesized;
  -  }
  -}
  -
   class _TypeSystemTypeOperations
       implements TypeOperations<VariableElement, DartType> {
     final TypeSystem typeSystem;
  
positive.code:     node.accept(_AssignedVariablesVisitor(assignedVariables));
  
      return FlowAnalysisHelper._(
          _NodeOperations(),
          _TypeSystemTypeOperations(typeSystem),
          assignedVariables,
          retainDataForTesting ? FlowAnalysisResult() : null);
  
negative.code:   }
  }
  
  /// The flow analysis based implementation of [LocalVariableTypeProvider].
  class _LocalVariableTypeProvider implements LocalVariableTypeProvider {
    final FlowAnalysisHelper _manager;
  