anchor.diff:    }
   }
   
  +typedef WatchEventPredicate = bool Function(WatchEvent event);
  +
   class PipelineWatcher {
     PipelineWatcher({
       @required this.dir,
       @required this.pipeline,
  +    this.ignore,
     }) : watcher = DirectoryWatcher(dir);
   
     /// The path of the directory to watch for changes.
  
positive.code:   Timer _scheduledPipeline;
  
    void _onEvent(WatchEvent event) {
      final String relativePath = path.relative(event.path, from: dir);
      print('- [${event.type}] ${relativePath}');
  
  
negative.code:       PipelineWatcher(
          dir: libPath.absolute,
          pipeline: buildPipeline,
          // Ignore font files that are copied whenever tests run.
          ignore: (event) => event.path.endsWith('.ttf'),
        ).start();
        // Return a never-ending future.
        return Completer<bool>().future;
  