anchor.diff:      var contextMap = byElementKind.putIfAbsent(context, () => {});
       var key = kind.name;
       contextMap[key] = (contextMap[key] ?? 0) + 1;
  +  }
  +
  +  /// Record that an identifier of the given [length] was found.
  +  void recordIdentifierOfLength(int length) {
  +    identifierLengths[length] = (identifierLengths[length] ?? 0) + 1;
     }
   
     /// Record information about the distance between recurring tokens.
  
positive.code:     }
    }
  
    /// Write the given [matrix] to the [sink]. The keys of the outer map will be
    /// the row titles; the keys of the inner map will be the column titles.
    void _writeMatrix(StringSink sink, Map<int, Map<int, int>> matrix) {
  
negative.code:   void visitSimpleFormalParameter(SimpleFormalParameter node) {
      // There are no completions.
      super.visitSimpleFormalParameter(node);
    }
  
    @override
    void visitSimpleIdentifier(SimpleIdentifier node) {
      data.recordIdentifierOfLength(node.name.length);
      super.visitSimpleIdentifier(node);
    }
  
    @override
  