anchor.diff:      var primaryId = transform.primaryId;
       transform.declareOutput(primaryId.addExtension(".js"));
       transform.declareOutput(primaryId.addExtension(".precompiled.js"));
  -    if (generateSourceMaps) {
  +    if (_generateSourceMaps) {
         transform.declareOutput(primaryId.addExtension(".js.map"));
       }
       return new Future.value();
  
positive.code:   /// Run the dart2js compiler.
    Future _doCompilation(Transform transform) {
      var provider = new _BarbackCompilerProvider(_environment, transform,
          generateSourceMaps: _settings.mode != BarbackMode.RELEASE);
  
      // Create a "path" to the entrypoint script. The entrypoint may not actually
      // be on disk, but this gives dart2js a root to resolve relative paths
  
negative.code: 
    final BuildEnvironment _environment;
    final BarbackSettings _settings;
  
    /// Whether source maps should be generated for the compiled JS.
    bool get _generateSourceMaps => _settings.mode != BarbackMode.RELEASE;
  
    Dart2JSTransformer.withSettings(this._environment, this._settings) {
      var invalidOptions = _settings.configuration.keys.toSet()
  