anchor.diff:      // The URI cannot be resolved, we don't know the library.
       if (librarySource == null) return null;
   
  -    var reader = libraryReaders[uriStr];
  +    var reader = _libraryReaders[uriStr];
       if (reader == null) {
         throw ArgumentError(
           'Missing library: $uriStr\n'
  -        'Available libraries: ${libraryReaders.keys.toList()}',
  +        'Available libraries: ${_libraryReaders.keys.toList()}',
         );
       }
   
  
positive.code:   void removeLibraries(Set<String> uriStrSet) {
      for (var uriStr in uriStrSet) {
        _exportsOfLibrary.remove(uriStr);
        libraryReaders.remove(uriStr);
        var libraryReference = rootReference.removeChild(uriStr);
        _invalidateLibrary(libraryReference);
      }
  
negative.code:   }
  
    bool get hasDartCore {
      return _libraryReaders.containsKey('dart:core');
    }
  
    void addBundle(BundleReader bundle) {
  