Make AudioDebugFileWriter create its own file worker thread.

content/browser/renderer_host/media/audio_input_renderer_host.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 "content/browser/renderer_host/media/audio_input_renderer_host.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 337 matching lines @@
     // For MEDIA_TAB_AUDIO_CAPTURE, the probable use case is Cast, we mute
     // the source audio.
     // TODO(qiangchen): Analyze audio constraints to make a duplicating or
     // diverting decision. It would give web developer more flexibility.
     entry->controller = media::AudioInputController::CreateForStream(
         audio_manager_->GetTaskRunner(), this,
         WebContentsAudioInputStream::Create(
             device_id, audio_params, audio_manager_->GetWorkerTaskRunner(),
             audio_mirroring_manager_),
         entry->writer.get(), user_input_monitor_,
-        BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE),
         audio_params);
     // Only count for captures from desktop media picker dialog.
     if (entry->controller.get() && type == MEDIA_DESKTOP_AUDIO_CAPTURE)
       IncrementDesktopCaptureCounter(TAB_AUDIO_CAPTURER_CREATED);
   } else {
     entry->controller = media::AudioInputController::Create(
         audio_manager_, this, entry->writer.get(), user_input_monitor_,
-        audio_params, device_id, config.automatic_gain_control,
-        BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE));
+        audio_params, device_id, config.automatic_gain_control);
     oss << ", AGC=" << config.automatic_gain_control;
 
     // Only count for captures from desktop media picker dialog and system loop
     // back audio.
     if (entry->controller.get() && type == MEDIA_DESKTOP_AUDIO_CAPTURE &&
         (device_id == media::AudioDeviceDescription::kLoopbackInputDeviceId ||
          device_id ==
              media::AudioDeviceDescription::kLoopbackWithMuteDeviceId)) {
       IncrementDesktopCaptureCounter(SYSTEM_LOOPBACK_AUDIO_CAPTURER_CREATED);
     }
@@ skipping 218 matching lines @@
     const base::FilePath& file,
     int stream_id) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   EnableDebugRecordingForId(GetDebugRecordingFilePathWithExtensions(file),
                             stream_id);
 }
 
 #endif  // BUILDFLAG(ENABLE_WEBRTC)
 
 }  // namespace content