anchor.diff:  import 'package:watcher/watcher.dart';
   
   import '../asset/id.dart';
  -import '../asset/writer.dart';
   import '../asset_graph/graph.dart';
   import '../asset_graph/node.dart';
   import '../logging/logging.dart';
  
positive.code:   WatchImpl(BuildOptions options, PhaseGroup phaseGroup)
        : _directoryWatcherFactory = options.directoryWatcherFactory,
          _debounceDelay = options.debounceDelay,
          _writer = options.writer,
          _packageGraph = options.packageGraph,
          _buildImpl = new BuildImpl(options, phaseGroup);
  
  
negative.code:   /// The [PackageGraph] for the current program.
    final PackageGraph _packageGraph;
  
    /// A future that completes when the current build is done.
    Future<BuildResult> _currentBuild;
    Future<BuildResult> get currentBuild => _currentBuild;
  