anchor.diff:  class Logger {
   
     final source;
  -  Function getMetaData;
     Level logLevel = null;
     Logger _parent;
     static StreamController _streamController =
  
positive.code:    * actual instance whenever it is called with the same string name.
     * Creates root logger with logLevel set if not created.
     */
    factory Logger(String source, {Map getMetaData()}) {
      return _loggers.putIfAbsent(source, source == "" ? _createRootLogger : () => new Logger._named(source));
    }
  
  
negative.code:    */
    static Stream<Map> get onRecord => _streamController.stream;
  
    static Function getMetaData;
  
    /**
     * All [Logger]s in the system.
     */
  