Make AudioDebugFileWriter create its own file worker thread.

media/audio/audio_debug_recording_manager.h

Index: media/audio/audio_debug_recording_manager.h
diff --git a/media/audio/audio_debug_recording_manager.h b/media/audio/audio_debug_recording_manager.h
index 2ea2a47a490d4fb5d0b10446b4d1abc54d93af71..750afca71387b5fa56c7fe59de820a235ae03766 100644
--- a/media/audio/audio_debug_recording_manager.h
+++ b/media/audio/audio_debug_recording_manager.h
@@ -61,8 +61,7 @@ class AudioDebugRecordingHelper;
 class MEDIA_EXPORT AudioDebugRecordingManager {
  public:
   AudioDebugRecordingManager(
-      scoped_refptr<base::SingleThreadTaskRunner> task_runner,
-      scoped_refptr<base::SingleThreadTaskRunner> file_task_runner);
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner);
   virtual ~AudioDebugRecordingManager();
 
   // Enables and disables debug recording.
@@ -81,7 +80,6 @@ class MEDIA_EXPORT AudioDebugRecordingManager {
   CreateAudioDebugRecordingHelper(
       const AudioParameters& params,
       scoped_refptr<base::SingleThreadTaskRunner> task_runner,
-      scoped_refptr<base::SingleThreadTaskRunner> file_task_runner,
       base::OnceClosure on_destruction_closure);
 
   // The task runner this class lives on. Also handed to
@@ -113,10 +111,6 @@ class MEDIA_EXPORT AudioDebugRecordingManager {
   // recording is enabled.
   base::FilePath debug_recording_base_file_name_;
 
-  // Task runner that the file writer does file output operations on. Handed to
-  // AudioDebugRecordingHelpers
-  scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
-
   base::WeakPtrFactory<AudioDebugRecordingManager> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(AudioDebugRecordingManager);
 };