Revert "remove serialization. it's moved to github"

pkg/serialization/test/no_library_test.dart

+// Copyright (c) 2013, 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.
+
+import 'package:serialization/serialization.dart';
+import 'package:unittest/unittest.dart';
+
+class Thing {
+  var name;
+}
+
+void main() {
+
+  test("Serializing something without a library directive", () {
+    var thing = new Thing()..name = 'testThing';
+    var s = new Serialization()
+      ..addRuleFor(Thing);
+    var serialized = s.write(thing);
+    var newThing = s.read(serialized);
+    expect(thing.name, newThing.name);
+  });
+}