Make AudioDebugFileWriter create its own file worker thread.

media/audio/audio_debug_file_writer.cc

 // Copyright 2015 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.
 
 #include "media/audio/audio_debug_file_writer.h"
 
 #include <stdint.h>
 #include <array>
 #include <utility>
 
@@ skipping 282 matching lines @@
   // fails, so it will continue to post data to be recorded, which won't
   // be written to the file. This also won't be reflected in WillWrite(). It's
   // fine, because this situation is rare, and all the posting is expected to
   // happen in case of success anyways. This allows us to save on thread hops
   // for error reporting and to avoid dealing with lifetime issues. It also
   // means file_.IsValid() should always be checked before issuing writes to it.
   PLOG(ERROR) << "Could not open debug recording file, error="
               << file_.error_details();
 }
 
-AudioDebugFileWriter::AudioDebugFileWriter(
-    const AudioParameters& params,
-    scoped_refptr<base::SingleThreadTaskRunner> file_task_runner)
-    : params_(params), file_task_runner_(std::move(file_task_runner)) {
+AudioDebugFileWriter::AudioDebugFileWriter(const AudioParameters& params)
+    : params_(params) {
   client_sequence_checker_.DetachFromSequence();
 }
 
 AudioDebugFileWriter::~AudioDebugFileWriter() {
   // |file_writer_| will be deleted on |task_runner_|.
 }
 
 void AudioDebugFileWriter::Start(const base::FilePath& file_name) {
   DCHECK(client_sequence_checker_.CalledOnValidSequence());
   DCHECK(!file_writer_);
@@ skipping 27 matching lines @@
   // here, but it's fine: we can afford missing some data or scheduling some
   // no-op writes.
   return !!file_writer_;
 }
 
 const base::FilePath::CharType* AudioDebugFileWriter::GetFileNameExtension() {
   return FILE_PATH_LITERAL("wav");
 }
 
 }  // namspace media