Add a new kind of suite to ease test.dart integration.

tools/testing/dart/package_testing_support.dart

+// Copyright (c) 2017, 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.md file.
+
+library package_testing_support;
+
+import 'dart:convert' show
+    JSON;
+
+import 'test_configurations.dart' show
+    testConfigurations;
+
+import 'test_options.dart' show
+    TestOptionsParser;
+
+import 'test_suite.dart' show
+    TestUtils;
+
+main(List<String> arguments) {
+  TestUtils.setDartDirUri(Uri.base);
+  List<Map> configurations = <Map>[];
+  for (String argument in arguments) {
+    configurations.addAll(new TestOptionsParser().parse(argument.split(" ")));
+  }
+  testConfigurations(configurations);
+}