[chromecast] Moves CastAudioOutputStream::Backend to CMA thread.

chromecast/media/audio/cast_audio_output_stream.h

Index: chromecast/media/audio/cast_audio_output_stream.h
diff --git a/chromecast/media/audio/cast_audio_output_stream.h b/chromecast/media/audio/cast_audio_output_stream.h
index 7d48e90dfda31a5e4183c49e686fc89e536f9d48..4a1d98d5397528a918e62b3793636fe057b659e0 100644
--- a/chromecast/media/audio/cast_audio_output_stream.h
+++ b/chromecast/media/audio/cast_audio_output_stream.h
@@ -8,17 +8,13 @@
 #include <memory>
 
 #include "base/macros.h"
-#include "base/memory/weak_ptr.h"
-#include "base/time/time.h"
 #include "media/audio/audio_io.h"
 #include "media/base/audio_parameters.h"
-#include "media/base/audio_timestamp_helper.h"
 
 namespace chromecast {
 namespace media {
 
 class CastAudioManager;
-class DecoderBufferBase;
 
 class CastAudioOutputStream : public ::media::AudioOutputStream {
  public:
@@ -37,23 +33,12 @@ class CastAudioOutputStream : public ::media::AudioOutputStream {
  private:
   class Backend;
 
-  void PushBuffer();
-  void OnPushBufferComplete(bool success);
-
   const ::media::AudioParameters audio_params_;
   CastAudioManager* const audio_manager_;
-
   double volume_;
-  AudioSourceCallback* source_callback_;
-  std::unique_ptr<::media::AudioBus> audio_bus_;
-  scoped_refptr<media::DecoderBufferBase> decoder_buffer_;
-  ::media::AudioTimestampHelper timestamp_helper_;
-  std::unique_ptr<Backend> backend_;
-  const base::TimeDelta buffer_duration_;
-  bool push_in_progress_;
-  base::TimeTicks next_push_time_;
 
-  base::WeakPtrFactory<CastAudioOutputStream> weak_factory_;
+  // Only valid when the stream is open.
+  std::unique_ptr<Backend> backend_;
 
   DISALLOW_COPY_AND_ASSIGN(CastAudioOutputStream);
 };