anchor.diff:        watchImpl.addFutureResult(new Future.value(new BuildResult(
             BuildStatus.success, [],
             performance: new BuildPerformanceTracker.noOp())));
  -      await new Future.value();
  +      await new Future(() {});
         var response = await serveHandler.handlerFor('web')(
             new Request('GET', Uri.parse(r'http://server.com/$perf')));
   
  
positive.code:   }
  
    MockWatchImpl(this.reader, this.packageGraph, this.assetGraph) {
      _futureBuildResultsController.stream.listen((futureBuildResult) {
        if (_currentBuild != null) {
          _currentBuild = _currentBuild.then((_) => futureBuildResult);
        } else {
          _currentBuild = futureBuildResult;
        }
  
        _currentBuild.then((result) {
          _buildResultsController.add(result);
          _currentBuild = null;
        });
      });
    }
  
  
negative.code:       actionTracker.stop();
        watchImpl.addFutureResult(new Future.value(
            new BuildResult(BuildStatus.success, [], performance: tracker)));
        await new Future(() {});
        var response = await serveHandler.handlerFor('web')(
            new Request('GET', Uri.parse(r'http://server.com/$perf')));
  
  