[chromecast] Pass media task runner to MediaPipelineBackendManager.

chromecast/media/audio/cast_audio_manager.h

Index: chromecast/media/audio/cast_audio_manager.h
diff --git a/chromecast/media/audio/cast_audio_manager.h b/chromecast/media/audio/cast_audio_manager.h
index f2cec7e1d556e0ef6f00e8a4889812546af44d99..dc8c7d5c262a9df1183e85b432d3819f7409a507 100644
--- a/chromecast/media/audio/cast_audio_manager.h
+++ b/chromecast/media/audio/cast_audio_manager.h
@@ -15,11 +15,14 @@ class TaskRunnerImpl;
 namespace media {
 
 class MediaPipelineBackend;
+class MediaPipelineBackendManager;
 struct MediaPipelineDeviceParams;
 
 class CastAudioManager : public ::media::AudioManagerBase {
  public:
-  explicit CastAudioManager(::media::AudioLogFactory* audio_log_factory);
+  // This class does not take ownership of |backend_manager|
+  CastAudioManager(::media::AudioLogFactory* audio_log_factory,
+                   MediaPipelineBackendManager* backend_manager);
   ~CastAudioManager() override;
 
   // AudioManager implementation.
@@ -53,6 +56,8 @@ class CastAudioManager : public ::media::AudioManagerBase {
       const std::string& output_device_id,
       const ::media::AudioParameters& input_params) override;
 
+  MediaPipelineBackendManager* const backend_manager_;
+
   DISALLOW_COPY_AND_ASSIGN(CastAudioManager);
 };