Expose Service Describer in Dart mojo package

mojo/dart/packages/mojo/lib/src/service_describer.dart

Index: mojo/dart/packages/mojo/lib/src/service_describer.dart
diff --git a/mojo/dart/packages/mojo/lib/src/service_describer.dart b/mojo/dart/packages/mojo/lib/src/service_describer.dart
new file mode 100644
index 0000000000000000000000000000000000000000..74be9983e5dc3e14f4ba2e600d5eba331c798d3b
--- /dev/null
+++ b/mojo/dart/packages/mojo/lib/src/service_describer.dart
@@ -0,0 +1,22 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+part of application;
+
+class _ServiceDescriberImpl implements service_describer.ServiceDescriber {
+  final HashMap<String, service_describer.ServiceDescription> _data;
+  service_describer.ServiceDescriberStub _stub;
+
+  _ServiceDescriberImpl(this._data, core.MojoMessagePipeEndpoint endpoint) {
+    _stub =
+        new service_describer.ServiceDescriberStub.fromEndpoint(endpoint, this);
+  }
+
+  void describeService(String interfaceName,
+      service_describer.ServiceDescriptionStub descriptionRequest) {
+    if (_data.containsKey(interfaceName)) {
+      descriptionRequest.impl = _data[interfaceName];
+    }
+  }
+}