Factor out AudioOutputDelegate from AudioRendererHost.

content/browser/renderer_host/media/audio_output_delegate.h

+// 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.
+
+#ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_OUTPUT_DELEGATE_H_
+#define CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_OUTPUT_DELEGATE_H_
+
+#include <memory>
+#include <string>
+
+#include "base/macros.h"
+#include "base/memory/shared_memory.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sync_socket.h"
+#include "content/browser/media/capture/audio_mirroring_manager.h"
+#include "content/browser/renderer_host/media/audio_sync_reader.h"
+#include "content/public/browser/media_observer.h"
+#include "media/audio/audio_logging.h"
+#include "media/audio/audio_output_controller.h"
+#include "media/base/audio_parameters.h"
+
+namespace content {
+
+// This class is operated on the IO thread.
+class CONTENT_EXPORT AudioOutputDelegate
+    : private media::AudioOutputController::EventHandler {
+ public:
+  class EventHandler {
+   public:
+    // Suitable for tracking the number of active streams.

[o1ka, 2016/11/22 13:24:03]

This comment is not clear. Just explain when it is called (and on which thread).

[Max Morin, 2016/11/22 16:04:29]

Done.

+    virtual void OnStreamStateChanged(bool playing) = 0;
+    // Called when construction is finished and the stream is ready for

[o1ka, 2016/11/22 13:24:03]

nit: everywhere: add a blank line between a method declaration and the next
method comment

[Max Morin, 2016/11/22 16:04:29]

Done.

+    // playout.
+    virtual void OnStreamCreated(int stream_id,
+                                 base::SharedMemory* shared_memory,
+                                 base::CancelableSyncSocket* socket) = 0;
+    // Called if stream encounters an error and has become unusable.
+    virtual void OnStreamError(int stream_id) = 0;
+  };
+
+  struct Deleter {
+    void operator()(AudioOutputDelegate* delegate);
+  };
+
+  using UniquePtr = std::unique_ptr<AudioOutputDelegate, Deleter>;
+
+  // |handler| must be valid until the moment that the UniquePtr destructor
+  // finishes.
+  static UniquePtr Create(EventHandler* handler,
+                          media::AudioManager* audio_manager,
+                          std::unique_ptr<media::AudioLog> audio_log,
+                          AudioMirroringManager* mirroring_manager,
+                          MediaObserver* media_observer,
+                          int stream_id,
+                          int render_frame_id,
+                          int render_process_id,
+                          const media::AudioParameters& params,
+                          const std::string& output_device_id);
+  ~AudioOutputDelegate() override;
+
+  // TODO(maxmorin): Remove this when crbug.com/647185 is closed.
+  // This function is used to provide control of the audio stream to

[o1ka, 2016/11/22 13:24:03]

I'm not sure if this is true. As far as I remember, webrtc extensions use it to
get some info only, and they do not control streams.

[Max Morin, 2016/11/22 16:04:29]

See
https://cs.chromium.org/chromium/src/chrome/browser/extensions/api/webrtc_aud...

[o1ka, 2016/11/22 21:48:16]

Acknowledged.

+  // WebrtcAudioPrivateGetActiveSinkFunction and others in the webrtc extension
+  // API. Since the controller is shared, this means that it might outlive the
+  // AudioOutputDelegate. In this case, it is still safe to call functions on
+  // the controller, but it will not do anything. The controller is also shared
+  // with AudioStreamMonitor.
+  const scoped_refptr<media::AudioOutputController>& controller() const {
+    return controller_;
+  }
+
+  int stream_id() const { return stream_id_; }
+
+  // Stream control:
+  void OnPlayStream();
+  void OnPauseStream();
+  void OnSetVolume(double volume);
+
+ private:
+  AudioOutputDelegate(EventHandler* handler,
+                      media::AudioManager* audio_manager,
+                      std::unique_ptr<media::AudioLog> audio_log,
+                      AudioMirroringManager* mirroring_manager,
+                      MediaObserver* media_observer,
+                      int stream_id,
+                      int render_frame_id,
+                      int render_process_id,
+                      const media::AudioParameters& params,
+                      const std::string& output_device_id);
+
+  // AudioOutputController::EventHandler implementation.
+  void OnControllerCreated() override;
+  void OnControllerPlaying() override;
+  void OnControllerPaused() override;
+  void OnControllerError() override;
+
+  void UpdatePlayingState(bool playing);
+
+  // |handler_| is null if we are in the process of destruction. In this
+  // case, we will not run any scheduled operations.

[o1ka, 2016/11/22 13:24:03]

Comment is not quite clear: scheduled where/for whom?

[Max Morin, 2016/11/22 16:04:29]

Done.

+  EventHandler* handler_;
+  std::unique_ptr<media::AudioLog> const audio_log_;
+  AudioMirroringManager* const mirroring_manager_;
+  std::unique_ptr<AudioSyncReader> reader_;
+  scoped_refptr<media::AudioOutputController> controller_;
+  const int stream_id_;
+  const int render_frame_id_;
+  const int render_process_id_;
+  // This flag ensures that we only send OnStreamStateChanged notifications

[o1ka, 2016/11/22 13:24:03]

not: add an empty line before (and in other similar places)

[Max Morin, 2016/11/22 16:04:29]

Done.

+  // and (de)register with the stream monitor when the state actually changes.
+  bool playing_ = false;
+  base::WeakPtrFactory<AudioOutputDelegate> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioOutputDelegate);
+};
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_OUTPUT_DELEGATE_H_