Enable language and isolate tests using the dart test runner.

tests/language/test_config.dart

+// Copyright (c) 2011, 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("language_test_config");
+
+#import("../../tools/testing/dart/test_suite.dart");
+
+class LanguageTestSuite extends StandardTestSuite {
+  LanguageTestSuite(Map configuration)
+      : super(configuration,
+              "tests/language/src",
+              ["tests/language/language.status"]);
+}