Increase barback scheduled_test timeout for many_parallel_transformers test.

pkg/barback/test/package_graph/many_parallel_transformers_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library barback.test.package_graph.transform_test;
 
 import 'package:barback/src/utils.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../utils.dart';
 
 main() {
   initConfig();
 
   test("handles many parallel transformers", () {
+    currentSchedule.timeout *= 3;
     var files = new List.generate(100, (i) => "app|$i.txt");
     var rewrite = new RewriteTransformer("txt", "out");
     initGraph(files, {"app": [[rewrite]]});
 
     // Pause and resume apply to simulate parallel long-running transformers.
     rewrite.pauseApply();
     updateSources(files);
     schedule(pumpEventQueue);
     rewrite.resumeApply();
 
     for (var i = 0; i < 100; i++) {
       expectAsset("app|$i.out", "$i.out");
     }
     buildShouldSucceed();
 
     expect(rewrite.maxParallelRuns, completion(equals(10)));
   });
 }