[Media Router] Add MediaSink subtypes

chrome/browser/media/router/mojo/media_router_traits_test_service.mojom

Index: chrome/browser/media/router/mojo/media_router_traits_test_service.mojom
diff --git a/chrome/browser/media/router/mojo/media_router_traits_test_service.mojom b/chrome/browser/media/router/mojo/media_router_traits_test_service.mojom
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index 0000000000000000000000000000000000000000..9229fd8a6a3259014817612e27fe3b6001b8f9f4
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+++ b/chrome/browser/media/router/mojo/media_router_traits_test_service.mojom
@@ -0,0 +1,14 @@
+// Copyright 2017 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 media_router.mojom;
+
+import "chrome/browser/media/router/mojo/media_router.mojom";
+
+// All functions on this interface echo their arguments to test StructTraits
+// serialization and deserialization.
+interface MediaRouterTraitsTestService {
+  [Sync]
+  EchoMediaSink(MediaSink s) => (MediaSink sink);
+};