Make AudioDebugFileWriter create its own file worker thread.

media/audio/audio_debug_recording_helper.cc

Index: media/audio/audio_debug_recording_helper.cc
diff --git a/media/audio/audio_debug_recording_helper.cc b/media/audio/audio_debug_recording_helper.cc
index af006303619c0f2a4d94004cbd7be8cc837d2f88..a21f12cfbaf5b27fa3ce4bd76b29f97e326b3e99 100644
--- a/media/audio/audio_debug_recording_helper.cc
+++ b/media/audio/audio_debug_recording_helper.cc
@@ -15,12 +15,10 @@ namespace media {
 AudioDebugRecordingHelper::AudioDebugRecordingHelper(
     const AudioParameters& params,
     scoped_refptr<base::SingleThreadTaskRunner> task_runner,
-    scoped_refptr<base::SingleThreadTaskRunner> file_task_runner,
     base::OnceClosure on_destruction_closure)
     : params_(params),
       recording_enabled_(0),
       task_runner_(std::move(task_runner)),
-      file_task_runner_(std::move(file_task_runner)),
       on_destruction_closure_(std::move(on_destruction_closure)),
       weak_factory_(this) {}
 
@@ -35,7 +33,7 @@ void AudioDebugRecordingHelper::EnableDebugRecording(
   DCHECK(!debug_writer_);
   DCHECK(!file_name.empty());
 
-  debug_writer_ = CreateAudioDebugFileWriter(params_, file_task_runner_);
+  debug_writer_ = CreateAudioDebugFileWriter(params_);
   debug_writer_->Start(
       file_name.AddExtension(debug_writer_->GetFileNameExtension()));
 
@@ -93,9 +91,8 @@ void AudioDebugRecordingHelper::DoWrite(std::unique_ptr<media::AudioBus> data) {
 
 std::unique_ptr<AudioDebugFileWriter>
 AudioDebugRecordingHelper::CreateAudioDebugFileWriter(
-    const AudioParameters& params,
-    scoped_refptr<base::SingleThreadTaskRunner> file_task_runner) {
-  return base::MakeUnique<AudioDebugFileWriter>(params, file_task_runner);
+    const AudioParameters& params) {
+  return base::MakeUnique<AudioDebugFileWriter>(params);
 }
 
 }  // namespace media