anchor.diff:    leg.Script readScript(Uri uri, [leg.ScriptTag node]) {
       if (uri.scheme == 'dart') {
         uri = translateDartUri(uri, node);
  +    } else if (uri.scheme == 'package') {
  +      uri = translatePackageUri(uri, node);
       }
       String text = "";
       try {
  
positive.code:   ReadUriFromString provider;
    DiagnosticHandler handler;
    Uri libraryRoot;
    List<String> options;
    bool mockableLibraryUsed = false;
  
  
negative.code:     return libraryRoot.resolve(path);
    }
  
    translatePackageUri(Uri uri, leg.ScriptTag node) =>
      packageRoot.resolve(uri.path);
  
    bool run(Uri uri) {
      try {
        packageRoot = uri.resolve('packages/');
        bool success = super.run(uri);
        for (final task in tasks) {
          log('${task.name} took ${task.timing}msec');
        }
        return success;
      } finally {
        packageRoot = null;
      }
    }
  
    void reportDiagnostic(leg.SourceSpan span, String message, bool fatal) {
  