Implement a trivial Mojo EchoService that can be connected to over DBus

mojo/services/dbus_echo/echo.mojom

Index: mojo/services/dbus_echo/echo.mojom
diff --git a/mojo/services/dbus_echo/echo.mojom b/mojo/services/dbus_echo/echo.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..c2ad42a7f7e7ee195679c50daf49b100bb62ddd1
--- /dev/null
+++ b/mojo/services/dbus_echo/echo.mojom
@@ -0,0 +1,16 @@
+// Copyright 2014 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.
+
+module mojo {
+
+[Peer=EchoClient]
+interface EchoService {
+  Echo(string to_echo) => (string echoed);
+};
+
+[Peer=EchoService]
+interface EchoClient {
+};
+
+}