anchor.diff:    // TODO(rnystrom): Do something cleaner for this, or eliminate those files.
     final entrypoints = new Set<AssetId>();
   
  +  /// If this is non-null, then the transformer is currently being applied, so
  +  /// subsequent calls to [apply] will wait for this to finish before
  +  /// proceeding.
  +  ///
  +  /// Dart2js uses lots of memory, so if we try to actually run compiles in
  +  /// parallel, it takes down the VM. Instead, the transformer will force
  +  /// all applies to be sequential. The tracking bug to do something better
  +  /// is here: https://code.google.com/p/dart/issues/detail?id=14730.
  +  Future _running;
  +
     Dart2JSTransformer(this._graph, {bool minify})
         : _minify = minify == true ? true : false;
   
  
positive.code:   }
  
    Future apply(Transform transform) {
      var stopwatch = new Stopwatch();
      stopwatch.start();
  
  
negative.code:         if (error is CompilerException) return;
          throw error;
        });
      }).whenComplete(() {
        completer.complete();
        _running = null;
      });
    }
  }
  