Add mojo interface+impl creation of audio streams.

content/common/media/renderer_audio_output_stream_factory.mojom

+// 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 content.mojom;
+
+import "media/mojo/interfaces/audio_output_stream.mojom";
+import "media/mojo/interfaces/audio_parameters.mojom";
+import "media/mojo/interfaces/media_types.mojom";
+
+// This interface is used to create output streams. The client supplies a
+// request for a stream provider, and then supplies the desired audio
+// parameters to that to create the stream.
+interface RendererAudioOutputStreamFactory {
+  // Used to request a device. The AudioOutputStreamProviderRequest will be
+  // bound to an AudioOutputStreamProvider implementation or closed
+  // (in case of an error).
+  RequestDeviceAuthorization(
+      media.mojom.AudioOutputStreamProvider& stream_provider_request,
+      int64 session_id,
+      string device_id) =>
+      (media.mojom.OutputDeviceStatus state,
+       media.mojom.AudioParameters output_params,
+       string matched_device_id);
+};