anchor.diff:  
         final ExternalReferences externals = library as ExternalReferences;
         for (final ExternalReference external
  -          in externals.children as Iterable<ExternalReference>) {
  -        assert(external.isExternal);
  -
  +          in externals.children.cast<ExternalReference>()) {
           final liveExternal = external.liveExternal;
           final size = liveExternal.externalProperty.externalSize;
           final liveElement = liveExternal.live;
  
positive.code:     var instanceIndex = 0;
      _debugMonitor('Class $name Instance=$instanceIndex');
      for (final ObjectReference objRef
          in classRef.children as Iterable<ObjectReference>) {
        final fields = objRef.instance.getFields();
        // Root __FIELDS__ is a container for children, the children
        // are added, later, to a treenode - if the treenode should
  
negative.code:     } else if (library.isLibrary) {
        final librariesToAnalyze = <ClassReference>[];
        for (final ClassReference classRef
            in library.children.cast<ClassReference>()) {
          final HeapGraphClassLive liveClass = classRef.actualClass!;
          if (_classMatcher(liveClass)) {
            librariesToAnalyze.add(classRef);
  