Add mojo interface+impl for audio stream control.

media/mojo/interfaces/audio_output.mojom

 // 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.
 
 module media.mojom;
 
 import "media/mojo/interfaces/audio_parameters.mojom";
+import "media/mojo/interfaces/media_types.mojom";
 
-// This interface handles audio output stream operations.
-// It allows to close a stream.
-// TODO(rchtara): Add methods that allow the interaction with audio output
-// streams: Play, Pause and SetVolume to this interface.
-// See crbug.com/606707 for more details.
-interface AudioOutputStream {
-  Close();
+// An interface for controlling an audio output stream.
+// On error, the message pipe is closed.
+// To close the stream, just close the message pipe.
+interface AudioOutput {

[DaleCurtis, 2017/03/06 17:56:12]

I think I prefer some sort of trailing differentiation; a la AudioOutputStream,
etc. Don't want to bike-shed too much, but AudiOutput feels too generic given
our overwhelming abundance of things with audio_output in the name.

[Max Morin, 2017/03/07 11:23:16]

Makes sense. Now AudioOutputStream.

[o1ka, 2017/03/07 13:04:53]

Don't we have one AudioOutputStream already?

+  // Starts rendering audio.
+  Play();
+  // Stops rendering audio and sends a signal to the |socket_descriptor|

[DaleCurtis, 2017/03/06 17:56:12]

Add blank lines between comments and methods.

[Max Morin, 2017/03/07 11:23:16]

Done.

+  // indicating this.
+  Pause();
+  // Sets volume. Volume must be in the range [0, 1].
+  SetVolume(double volume);
 };
 
-// This interface manages audio output streams.
-// It allows to create an AudioOutputStream.
-// TODO(rchtara): Add a method to request device authorization to this
-// interface.
-// See crbug.com/606707 for more details.
-interface AudioOutput {
-  // TODO(rchtara): Remove |stream_id| from AudioOutput::CreateStream when all
-  // the stream operations are mojofied.
-  CreateStream(
-      int32 stream_id,
-      AudioParameters params) =>
-      (int32 stream_id,
-       AudioOutputStream? stream,
-       handle<shared_buffer>? shared_buffer,
-       handle? socket_descriptor);
-};
+interface AudioOutputProvider {
+  // Creates a new AudioOutput using |params|. |shared_buffer| and
+  // |socket_descriptor| are used to write data to the stream as defined
+  // in AudioDeviceThread. Can only be used for one output stream.
+  Acquire(AudioOutput&? audio_output, media.mojom.AudioParameters params) =>

[DaleCurtis, 2017/03/06 17:56:12]

Hmm, why this signature versus:

Acquire(params) => (AudioOutput, handle, handle) ?

[Max Morin, 2017/03/07 11:23:16]

I prefer this one since it allows things like:

AudioOutputPtr output;
Acquire(mojo::MakeRequest(&output), params, callback);
// No need to wait for callback:
output->SetVolume(0.5);

If we got the outputptr in the callback instead, we'd have to buffer the calls
manually while waiting for the callback.

+       (handle<shared_buffer> shared_buffer,
+        handle socket_descriptor);
+};