Replace the configuration map with a typed object.

tools/testing/dart/package_testing_support.dart

Index: tools/testing/dart/package_testing_support.dart
diff --git a/tools/testing/dart/package_testing_support.dart b/tools/testing/dart/package_testing_support.dart
index 828147690d12bb3421b35f92ab4988de6813b890..ff98f30982bf9f4b52fdf46f25c4c0add0185001 100644
--- a/tools/testing/dart/package_testing_support.dart
+++ b/tools/testing/dart/package_testing_support.dart
@@ -2,15 +2,14 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
-library package_testing_support;
-
+import 'configuration.dart';
 import 'options.dart';
 import 'test_configurations.dart';
 import 'test_suite.dart';
 
 void main(List<String> arguments) {
   TestUtils.setDartDirUri(Uri.base);
-  var configurations = <Map<String, dynamic>>[];
+  var configurations = <Configuration>[];
   for (var argument in arguments) {
     configurations.addAll(new OptionsParser().parse(argument.split(" ")));
   }