Add a sky media service to make it possible to play a sound.

sky/services/media/media.mojom

Index: sky/services/media/media.mojom
diff --git a/sky/services/media/media.mojom b/sky/services/media/media.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..ab6edcb48b546e018cde68b49025586f51f87a0a
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+++ b/sky/services/media/media.mojom
@@ -0,0 +1,17 @@
+// Copyright 2015 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;
+
+interface MediaPlayer {
+  // ignored argument due to https://github.com/domokit/mojo/issues/282
+  Prepare(handle<data_pipe_consumer> data_source) => (bool ignored);
+  Start();
+  Pause();
+  SeekTo(uint32 msec);
+};
+
+interface MediaService {
+  CreatePlayer(MediaPlayer& player);
+};