Make AudioDebugFileWriter create its own file worker thread.

content/browser/speech/speech_recognizer_impl.cc

Index: content/browser/speech/speech_recognizer_impl.cc
diff --git a/content/browser/speech/speech_recognizer_impl.cc b/content/browser/speech/speech_recognizer_impl.cc
index ec05e3154cfdb80630643d8fe926d9efd62999dc..45dd6c3352ed059a143693b0f6478efa81ed28ec 100644
--- a/content/browser/speech/speech_recognizer_impl.cc
+++ b/content/browser/speech/speech_recognizer_impl.cc
@@ -10,6 +10,7 @@
 
 #include "base/bind.h"
 #include "base/macros.h"
+#include "base/task_scheduler/post_task.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "content/browser/browser_main_loop.h"
@@ -638,7 +639,8 @@ SpeechRecognizerImpl::StartRecording(const FSMEventArgs&) {
   audio_controller_ = AudioInputController::Create(

[fdoray, 2017/05/17 14:58:52]

The TaskRunner ends up being used here:
https://cs.chromium.org/chromium/src/media/audio/audio_debug_file_writer.h. We
shouldn't pass TaskRunners through several components. Instead, the component
that uses a TaskRunner should be the one that creates it. 

I think it would be worth it to remove the TaskRunner argument from all function
calls between here and the constructor of AudioDebugFileWriter. Then, we could
add a link to this CL in
https://chromium.googlesource.com/chromium/src/+/781747b0aa041e426b6446bd49c1...
to demonstrate best practices. (You will get points for all the files that you
have touched + 5 extra points for adding a link to the CL in the documentation).

       GetAudioManager(), this, this, nullptr, input_parameters, device_id_,
       /*agc_is_enabled*/ false,
-      BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE));
+      base::CreateSingleThreadTaskRunnerWithTraits(
+          {base::MayBlock(), base::TaskPriority::BACKGROUND}));
 
   if (!audio_controller_.get()) {
     return Abort(