Rejigger audio capture pipeline to work with separate main+worker threads (Mac).

media/audio/virtual_audio_output_stream.h

 // Copyright (c) 2012 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_VIRTUAL_AUDIO_OUTPUT_STREAM_H_
 #define MEDIA_AUDIO_VIRTUAL_AUDIO_OUTPUT_STREAM_H_
 
 #include "base/callback.h"
+#include "base/threading/thread_checker.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_parameters.h"
 #include "media/base/audio_converter.h"
 
-namespace base {
-class MessageLoopProxy;
-}
-
 namespace media {
 
 class VirtualAudioInputStream;
 
 // VirtualAudioOutputStream attaches to a VirtualAudioInputStream when Start()
 // is called and is used as an audio source. VirtualAudioOutputStream also
 // implements an interface so it can be used as an input to AudioConverter so
 // that we can get audio frames that match the AudioParameters that
 // VirtualAudioInputStream expects.
 class MEDIA_EXPORT VirtualAudioOutputStream
     : public AudioOutputStream,
       public AudioConverter::InputCallback {
  public:
   // Callback invoked just after VirtualAudioOutputStream is closed.
   typedef base::Callback<void(VirtualAudioOutputStream* vaos)>
       AfterCloseCallback;
 
   // Construct an audio loopback pathway to the given |target| (not owned).
   // |target| must outlive this instance.
   VirtualAudioOutputStream(const AudioParameters& params,
-                           base::MessageLoopProxy* message_loop,
                            VirtualAudioInputStream* target,
                            const AfterCloseCallback& after_close_cb);
 
   virtual ~VirtualAudioOutputStream();
 
   // AudioOutputStream:
   virtual bool Open() OVERRIDE;
   virtual void Start(AudioSourceCallback* callback) OVERRIDE;
   virtual void Stop() OVERRIDE;
   virtual void SetVolume(double volume) OVERRIDE;
   virtual void GetVolume(double* volume) OVERRIDE;
   virtual void Close() OVERRIDE;
 
  private:
   // AudioConverter::InputCallback:
   virtual double ProvideInput(AudioBus* audio_bus,
                               base::TimeDelta buffer_delay) OVERRIDE;
 
   const AudioParameters params_;
-  base::MessageLoopProxy* const message_loop_;
   // Pointer to the VirtualAudioInputStream to attach to when Start() is called.
   // This pointer should always be valid because VirtualAudioInputStream should
   // outlive this class.
   VirtualAudioInputStream* const target_input_stream_;
 
   AfterCloseCallback after_close_cb_;
 
   AudioSourceCallback* callback_;
   double volume_;
 
+  base::ThreadChecker thread_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(VirtualAudioOutputStream);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_VIRTUAL_AUDIO_OUTPUT_STREAM_H_