Mojo interfaces needed for switching audio rendering stream creation and closing from IPC to Mojo

content/common/media/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;

[xhwang, 2016/05/06 16:27:29]

This should be in content.mojom now.

[rchtara, 2016/05/09 15:14:58]

Done.

+
+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();
+};
+
+// This interface manages audio output streams.
+// It allows to create an AudioOutputStream.
+// TODO(rchtara): Add method to request a device authorization to this
+// interface.
+// See crbug.com/606707 for more details.
+interface AudioOutput {
+  CreateStream(
+      int32 stream_id,
+      int32 render_frame_id,
+      media.interfaces.AudioParameters params) =>
+      (int32 stream_id,
+       AudioOutputStream? stream,
+       handle<shared_buffer>? shared_buffer,
+       handle? socket_descriptor);
+   // Used to close streams which are just authorized but not created yet.
+   CloseStream(int32 stream_id);

[xhwang, 2016/05/06 16:27:29]

Typically in mojo world when the connection is dropped the interface
implementation will be closed. But I don't know enough detail here to give
better suggestions.

Also, this CloseStream() call is related to authorization. But it seems
authorization is still TODO. Shall we add this call later? From this current API
I can't really see how CloseStream() could be used.

[rchtara, 2016/05/09 15:14:58]

We were planning to take advantage of that to report errors from the browser to
the renderer as reporting errors is more complicated than Closing the stream.
* closing stream is the simplest operation we are going to do: we dont even have
to return anything from the renderer to the browser.
https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/re...

* SendErrorMessage is used 7 times in audio_renderer_host.cc (after creating
stream, playing it,pausing it). So the plan is to drop the connection after we
found an error in the browser, so the renderer  is going to be notified that
there is an error. 

https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/re...
The reason why it's included here is that I want to get rid of all the
AudioHostMsg_CloseStream after this cl and cl 1930393002 land.

PS: This is something temporary and the new plan will be to remove CloseStream
form AudioOutput when RequestDeviceAuthorization lands and replace it with a new
create method in AudioOutputStream: 
A AudioOutputStreamPtr will be directly returned after
RequestDeviceAuthorization call.
Then you can call Create (which is a new member method of AudioOutputStream) on
the AudioOutputStreamPtr to do the equivalent of AudioHostMsg_CreateStream.
If you want to close the stream you can call Close with or without calling
Create.

See please updated interface
(https://docs.google.com/document/d/1wE5dNDPZE1OGMuEkKvRiRxlrV_50DJqUvQBkvJEqy...)

+};