Make AudioDebugFileWriter create its own file worker thread.

media/audio/audio_input_controller_unittest.cc

Index: media/audio/audio_input_controller_unittest.cc
diff --git a/media/audio/audio_input_controller_unittest.cc b/media/audio/audio_input_controller_unittest.cc
index 65d56417c53df67328848ea41d9cc7814790c484..3d9ba1a98030ed61b3e54f3f7ceb14a58462cc54 100644
--- a/media/audio/audio_input_controller_unittest.cc
+++ b/media/audio/audio_input_controller_unittest.cc
@@ -128,7 +128,7 @@ TEST_F(AudioInputControllerTest, CreateAndClose) {
   SuspendAudioThread();
   controller = AudioInputController::Create(
       audio_manager_.get(), &event_handler, &sync_writer, nullptr, params,
-      AudioDeviceDescription::kDefaultDeviceId, false, audio_task_runner());
+      AudioDeviceDescription::kDefaultDeviceId, false);
   ASSERT_TRUE(controller.get());
   EXPECT_CALL(event_handler, OnCreated(controller.get())).Times(Exactly(1));
   EXPECT_CALL(event_handler, OnLog(controller.get(), _));
@@ -163,7 +163,7 @@ TEST_F(AudioInputControllerTest, RecordAndClose) {
   // Creating the AudioInputController should render an OnCreated() call.
   scoped_refptr<AudioInputController> controller = AudioInputController::Create(
       audio_manager_.get(), &event_handler, &sync_writer, nullptr, params,
-      AudioDeviceDescription::kDefaultDeviceId, false, audio_task_runner());
+      AudioDeviceDescription::kDefaultDeviceId, false);
   ASSERT_TRUE(controller.get());
 
   controller->Record();
@@ -189,7 +189,7 @@ TEST_F(AudioInputControllerTest, SamplesPerPacketTooLarge) {
                          kSamplesPerPacket * 1000);
   scoped_refptr<AudioInputController> controller = AudioInputController::Create(
       audio_manager_.get(), &event_handler, &sync_writer, nullptr, params,
-      AudioDeviceDescription::kDefaultDeviceId, false, audio_task_runner());
+      AudioDeviceDescription::kDefaultDeviceId, false);
   ASSERT_FALSE(controller.get());
 }
 
@@ -211,7 +211,7 @@ TEST_F(AudioInputControllerTest, CloseTwice) {
                          kSamplesPerPacket);
   scoped_refptr<AudioInputController> controller = AudioInputController::Create(
       audio_manager_.get(), &event_handler, &sync_writer, nullptr, params,
-      AudioDeviceDescription::kDefaultDeviceId, false, audio_task_runner());
+      AudioDeviceDescription::kDefaultDeviceId, false);
   ASSERT_TRUE(controller.get());
 
   controller->Record();