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 AudioOutputDelegate : private media::AudioOutputController::EventHandler {
+ public:
+  class EventHandler {
+   public:
+    // Only called when playing-state changes.
+    virtual void OnStreamStateChanged(bool playing) = 0;
+    // Called when construction is finished and the stream is ready for
+    // 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;
+  };
+
+  AudioOutputDelegate(EventHandler* handler,
+                      std::unique_ptr<media::AudioLog> audio_log,
+                      AudioMirroringManager* mirroring_manager,
+                      MediaObserver* media_observer,
+                      int stream_id,
+                      int render_frame_id,
+                      int render_process_id,
+                      media::AudioParameters params,
+                      const std::string& output_device_id);
+  ~AudioOutputDelegate() override;
+
+  const scoped_refptr<media::AudioOutputController>& controller() const {
+    return controller_;
+  }
+
+  int stream_id() const { return stream_id_; }
+
+  // Stream control:
+  void OnPlayStream();
+  void OnPauseStream();
+  // The ownership of this object is passed into the method.
+  // It will delete itself when ready. After this has been called,

[o1ka, 2016/10/26 13:11:48]

I would remove "when ready" sentence: it's a bit confusing.

+  // the AudioOutputDelegate will no longer call any methods on the event
+  // handler.
+  void OnCloseStream(std::unique_ptr<AudioOutputDelegate> owned_this);

[o1ka, 2016/10/26 13:11:48]

Probably implement this as a deleter? It's deleter semantic anyways. Then we can
"hide" the destructor from the users, and thus will guarantee that
FinishClosing() logic is executed before (or rather during) destruction.

+  void OnSetVolume(double volume);
+
+ private:
+  // AudioOutputController::EventHandler implementation.
+  void OnControllerCreated() override;
+  void OnControllerPlaying() override;
+  void OnControllerPaused() override;
+  void OnControllerError() override;
+
+  void FinishClosing();

[o1ka, 2016/10/26 13:11:48]

I do not quite like this name, but I'm bad in naming :( Probably just "Close"? 

+  void UpdatePlayingStateForHandler(bool playing);
+
+  EventHandler* const 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
+  // when the state actually changes.
+  bool playing_ = false;
+  // This flag ensures we don't send events to handler_ after OnStreamClosed.
+  bool closed_ = false;

[o1ka, 2016/10/26 13:11:48]

Looks like there is no need for the flag: we can just reset handler_ to nullptr
- it's always accessed on the same thread.

+  base::WeakPtrFactory<AudioOutputDelegate> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioOutputDelegate);
+};
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_AUDIO_OUTPUT_DELEGATE_H_