anchor.diff:    final ErrorReporter _errorReporter;
   
     /// The object used to track the usage of labels within a given label scope.
  -  _LabelTracker? labelTracker;
  +  _LabelTracker? _labelTracker;
   
     DeadCodeVerifier(this._errorReporter);
   
     @override
     void visitBreakStatement(BreakStatement node) {
  -    labelTracker?.recordUsage(node.label?.name);
  +    _labelTracker?.recordUsage(node.label?.name);
     }
   
     @override
     void visitContinueStatement(ContinueStatement node) {
  -    labelTracker?.recordUsage(node.label?.name);
  +    _labelTracker?.recordUsage(node.label?.name);
     }
   
     @override
  
positive.code:           }
          }
  
          var offset = _firstDeadNode!.offset;
          var length = node.end - offset;
          _errorReporter.reportErrorForOffset(HintCode.DEAD_CODE, offset, length);
        }
  
negative.code:   /// not `null`, and is covered by the [node], then we reached the end of
    /// the current dead code interval.
    void flowEnd(AstNode node) {
      var firstDeadNode = _firstDeadNode;
      if (firstDeadNode != null) {
        if (!_containsFirstDeadNode(node)) {
          return;
        }
  
        var parent = firstDeadNode.parent;
        if (parent is Assertion && identical(firstDeadNode, parent.message)) {
          // Don't report "dead code" for the message part of an assert statement,
          // because this causes nuisance warnings for redundant `!= null`
          // asserts.
  