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:       actionTracker.stop();
        watchImpl.addFutureResult(new Future.value(
            new BuildResult(BuildStatus.success, [], performance: tracker)));
        await new Future.value();
        var response = await serveHandler.handlerFor('web')(
            new Request('GET', Uri.parse(r'http://server.com/$perf')));
  
  
negative.code:   }
  
    MockWatchImpl(this.reader, this.packageGraph, this.assetGraph) {
      var firstBuild = new Completer<BuildResult>();
      _currentBuild = firstBuild.future;
      _futureBuildResultsController.stream.listen((futureBuildResult) {
        if (!firstBuild.isCompleted) {
          firstBuild.complete(futureBuildResult);
        }
        _currentBuild = _currentBuild.then((_) => futureBuildResult);
        _currentBuild.then(_buildResultsController.add);
      });
    }
  
  