Switch Speech Recognition to asynchronous callback-based AudioManager interactions.

media/audio/audio_system.h

+// 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.
+
+#ifndef MEDIA_AUDIO_AUDIO_SYSTEM_H_
+#define MEDIA_AUDIO_AUDIO_SYSTEM_H_
+
+#include "base/callback.h"
+#include "media/audio/audio_device_description.h"
+#include "media/base/audio_parameters.h"
+#include "media/base/media_export.h"
+
+namespace media {
+class AudioManager;
+
+// Work in progress: Provides asynchronous interface to AudioManager. All the
+// AudioManager clients will be switched to it, in preparation for moving
+// to Mojo audio service.
+class MEDIA_EXPORT AudioSystem {

[tommi (sloooow) - chröme, 2017/02/02 16:27:18]

I feel that adding a new class at the same level as AudioManager, will cause
confusion.  Can we instead add GetInputStreamParametersAsync to AudioManager? 
Alternatively, we could rename the old one to 'Deprecated' and use
GetInputStreamParameters where we use the async variant.

[o1ka, 2017/02/02 16:32:22]

This is a staged switch to Mojo audio service (see CL description). AudioManager
interface won't be public soon.

+ public:
+  // Replies are asynchronously sent to the thread the call is issued on.
+  using OnAudioParamsCallback = base::Callback<void(const AudioParameters&)>;
+
+  virtual base::SingleThreadTaskRunner* GetTaskRunner() const = 0;
+
+  // Callback will receive invalid parameters if the device is not found.
+  virtual void GetInputStreamParameters(const std::string& device_id,
+                                        OnAudioParamsCallback on_params_cb) = 0;
+
+  // Must not be used for anything but stream creation.
+  virtual AudioManager* GetAudioManager() = 0;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_AUDIO_SYSTEM_H_