[chromecast] Pass media task runner to MediaPipelineBackendManager.

chromecast/media/audio/cast_audio_manager_factory.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 "chromecast/media/audio/cast_audio_manager_factory.h"
 
 #include "chromecast/media/audio/cast_audio_manager.h"
+#include "chromecast/media/cma/backend/media_pipeline_backend_manager.h"
 
 namespace chromecast {
 namespace media {
 
-CastAudioManagerFactory::CastAudioManagerFactory() {}
+CastAudioManagerFactory::CastAudioManagerFactory(
+    MediaPipelineBackendManager* backend_manager)
+    : backend_manager_(backend_manager) {
+}
 
 CastAudioManagerFactory::~CastAudioManagerFactory() {}
 
 ::media::AudioManager* CastAudioManagerFactory::CreateInstance(
     ::media::AudioLogFactory* audio_log_factory) {
-  return new CastAudioManager(audio_log_factory);
+  return new CastAudioManager(audio_log_factory, backend_manager_);
 }
 
 }  // namespace media
 }  // namespace chromecast