Revert of [chromecast] Pass media task runner to MediaPipelineBackendManager.

chromecast/media/audio/cast_audio_manager_factory.cc

Index: chromecast/media/audio/cast_audio_manager_factory.cc
diff --git a/chromecast/media/audio/cast_audio_manager_factory.cc b/chromecast/media/audio/cast_audio_manager_factory.cc
index c932c4b439bb90672c827889d689a8caac24cb24..7151f2139f01389d9b0f3f2cead7e9e1d9fb594c 100644
--- a/chromecast/media/audio/cast_audio_manager_factory.cc
+++ b/chromecast/media/audio/cast_audio_manager_factory.cc
@@ -5,21 +5,17 @@
 #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(
-    MediaPipelineBackendManager* backend_manager)
-    : backend_manager_(backend_manager) {
-}
+CastAudioManagerFactory::CastAudioManagerFactory() {}
 
 CastAudioManagerFactory::~CastAudioManagerFactory() {}
 
 ::media::AudioManager* CastAudioManagerFactory::CreateInstance(
     ::media::AudioLogFactory* audio_log_factory) {
-  return new CastAudioManager(audio_log_factory, backend_manager_);
+  return new CastAudioManager(audio_log_factory);
 }
 
 }  // namespace media