anchor.diff:        case 'externals':
           final externalsNode = AnalysisReference('Externals');
           analysisSnapshot.addChild(externalsNode);
  -        for (final ExternalReference ref
  -            in value as Iterable<ExternalReference>) {
  +        for (final ExternalReference ref in value.cast<ExternalReference>()) {
             final HeapGraphExternalLive liveExternal = ref.liveExternal;
             final HeapGraphElementLive liveElement = liveExternal.live;
   
  
positive.code:     } else if (library.isLibrary) {
        final librariesToAnalyze = <ClassReference>[];
        for (final ClassReference classRef
            in library.children as Iterable<ClassReference>) {
          final HeapGraphClassLive liveClass = classRef.actualClass!;
          if (_classMatcher(liveClass)) {
            librariesToAnalyze.add(classRef);
  
negative.code: 
        final ExternalReferences externals = library as ExternalReferences;
        for (final ExternalReference external
            in externals.children.cast<ExternalReference>()) {
          final liveExternal = external.liveExternal;
          final size = liveExternal.externalProperty.externalSize;
          final liveElement = liveExternal.live;
  