Make AudioDebugFileWriter create its own file worker thread.

media/audio/mock_audio_manager.cc

 // 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.
 
 #include "media/audio/mock_audio_manager.h"
 
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
 #include "media/base/audio_parameters.h"
@@ skipping 95 matching lines @@
   return get_associated_output_device_id_cb_.is_null()
              ? std::string()
              : get_associated_output_device_id_cb_.Run(input_device_id);
 }
 
 std::unique_ptr<AudioLog> MockAudioManager::CreateAudioLog(
     AudioLogFactory::AudioComponent component) {
   return nullptr;
 }
 
-void MockAudioManager::InitializeOutputDebugRecording(
-    scoped_refptr<base::SingleThreadTaskRunner> file_task_runner) {}
+void MockAudioManager::InitializeOutputDebugRecording() {}
 
 void MockAudioManager::EnableOutputDebugRecording(
     const base::FilePath& base_file_name) {}
 
 void MockAudioManager::DisableOutputDebugRecording() {}
 
 const char* MockAudioManager::GetName() {
   return nullptr;
 }
 
@@ skipping 28 matching lines @@
     GetDeviceDescriptionsCallback callback) {
   get_output_device_descriptions_cb_ = std::move(callback);
 }
 
 void MockAudioManager::SetAssociatedOutputDeviceIDCallback(
     GetAssociatedOutputDeviceIDCallback callback) {
   get_associated_output_device_id_cb_ = std::move(callback);
 }
 
 }  // namespace media.