Add support for package spec to testing HttpServer.

tools/testing/dart/test_configurations.dart

Index: tools/testing/dart/test_configurations.dart
diff --git a/tools/testing/dart/test_configurations.dart b/tools/testing/dart/test_configurations.dart
index 47e233be7987a8e13de86b07957a5a5b0edded94..f82e62dad599a40f76d319eecd58b0743b9e6384 100644
--- a/tools/testing/dart/test_configurations.dart
+++ b/tools/testing/dart/test_configurations.dart
@@ -132,11 +132,12 @@ Future testConfigurations(List<Map> configurations) async {
       // server for cross-domain tests can be found by calling
       // getCrossOriginPortNumber().
       var servers = new TestingServers(
-          new Path(TestUtils.buildDir(conf)),
+          TestUtils.buildDir(conf),
           useContentSecurityPolicy,
           conf['runtime'],
           null,
-          conf['package_root']);
+          conf['package_root'],
+          conf['packages']);
       serverFutures.add(servers.startServers(conf['local_ip'],
           port: conf['test_server_port'],
           crossOriginPort: conf['test_server_cross_origin_port']));