Add mojo interface+impl for audio stream control.

media/mojo/interfaces/audio_output.mojom

Index: media/mojo/interfaces/audio_output.mojom
diff --git a/media/mojo/interfaces/audio_output.mojom b/media/mojo/interfaces/audio_output.mojom
index 895a93e4967727e4d2846679b50433a2de46ff94..8d206c1cef3e4298c4ac6764e53b448890c711d9 100644
--- a/media/mojo/interfaces/audio_output.mojom
+++ b/media/mojo/interfaces/audio_output.mojom
@@ -5,29 +5,17 @@
 module media.mojom;
 
 import "media/mojo/interfaces/audio_parameters.mojom";
+import "media/mojo/interfaces/media_types.mojom";
+import "url/mojo/origin.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();
-};
-
-// 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.
+// On error, the message pipe is closed.
+// To close the stream, just close the message pipe.
 interface AudioOutput {

[DaleCurtis, 2017/02/21 18:18:32]

Can you fill these comments out now? I.e., high level class comment, and per
method comments describing the parameters and how they're used. Why we have
Start,Play,Pause.

That said, maybe we should rename Start to Initialize or Create? Just something
that doesn't imply the stream will start rendering w/o a play call.

[Max Morin, 2017/02/22 10:08:43]

Added comments, changed to Initialize.

[DaleCurtis, 2017/02/22 18:13:37]

After I wrote this, I got this feedback on my own mojo CL:

https://codereview.chromium.org/2687583002#msg18

See c#18 if it doesn't link directly there. Essentially mojo folk prefer
interfaces w/o an explicit initialize method so you can never do it wrong. They
suggest An AudioOutputProvider interface which vends AudioOutputRequest objects.

-  // 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);
-};
+  Start(media.mojom.AudioParameters params) =>
+       (handle<shared_buffer> shared_buffer,
+        handle socket_descriptor);
+  Play();
+  Pause();
+  // Volume is in the range [0, 1].
+  SetVolume(double volume);
+};