Support dart2js in pub serve.

sdk/lib/_internal/pub/test/transformer/dart2js/compiles_generated_dart_file_test.dart

Index: sdk/lib/_internal/pub/test/transformer/dart2js/compiles_generated_dart_file_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/dart2js/compiles_generated_dart_file_test.dart b/sdk/lib/_internal/pub/test/transformer/dart2js/compiles_generated_dart_file_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..399c2ce0a529edf3b8896d3b8b971f449ddf6e3c
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/transformer/dart2js/compiles_generated_dart_file_test.dart
@@ -0,0 +1,39 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 pub_tests;
+
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+import '../../serve/utils.dart';
+
+main() {
+  initConfig();
+  integration("compiles a generated Dart file to JS", () {
+    d.dir(appPath, [
+      d.pubspec({
+        "name": "myapp",
+        "version": "0.0.1",
+        "transformers": ["myapp/transformer"]
+      }),
+      d.dir("lib", [
+        d.file("transformer.dart", dartTransformer("munge"))
+      ]),
+      d.dir("web", [
+        d.file("main.dart", """
+const TOKEN = "before";
+void main() => print(TOKEN);
+""")
+      ])
+    ]).create();
+
+    createLockFile('myapp', pkg: ['barback']);
+
+    startPubServe();
+    requestShouldSucceed("main.dart.js", contains("(before, munge)"));
+    endPubServe();
+  });
+}