anchor.diff:        vmService.HeapSnapshotGraph graph) {
       for (vmService.HeapSnapshotField field in class_.fields) {
         if (field.name == name) {
  -        int index = o.references[field.index] - 1;
  +        int index = o.references[field.index];
           if (index < 0) {
             // Sentinel object.
             return null;
  
positive.code:         // Class is not interesting.
          continue;
        }
        vmService.HeapSnapshotClass c = graph.classes[o.classId - 1];
        Map<String, List<String>> interests = _interests[c.libraryUri];
        if (interests == null || interests.isEmpty) {
          // Not an object we care about.
  
negative.code:       vmService.HeapSnapshotObject o,
        vmService.HeapSnapshotGraph graph,
        Map<Uri, Map<String, List<String>>> prettyPrints) {
      if (o.classId <= 0) {
        return "Class sentinel";
      }
      vmService.HeapSnapshotClass class_ = o.klass;
  
      if (class_.name == "_OneByteString") {
        return '"${o.data}"';
  