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

chromecast/browser/cast_browser_main_parts.h

Index: chromecast/browser/cast_browser_main_parts.h
diff --git a/chromecast/browser/cast_browser_main_parts.h b/chromecast/browser/cast_browser_main_parts.h
index 5c6e3ee64442bf6de1b8ccd427ae1ff46d92dc12..1466b047164c543687f85e29c0d15740f3cad805 100644
--- a/chromecast/browser/cast_browser_main_parts.h
+++ b/chromecast/browser/cast_browser_main_parts.h
@@ -22,7 +22,6 @@
 namespace chromecast {
 
 namespace media {
-class MediaPipelineBackendManager;
 class MediaResourceTracker;
 class VideoPlaneController;
 }  // namespace media
@@ -39,10 +38,8 @@
   ~CastBrowserMainParts() override;
 
   scoped_refptr<base::SingleThreadTaskRunner> GetMediaTaskRunner() const;
-
 #if !defined(OS_ANDROID)
   media::MediaResourceTracker* media_resource_tracker();
-  media::MediaPipelineBackendManager* media_pipeline_backend_manager();
 #endif
 
   // content::BrowserMainParts implementation:
@@ -65,10 +62,6 @@
 #if !defined(OS_ANDROID)
   // Tracks usage of media resource by e.g. CMA pipeline, CDM.
   media::MediaResourceTracker* media_resource_tracker_;
-
-  // Tracks all media pipeline backends.
-  scoped_ptr<media::MediaPipelineBackendManager>
-      media_pipeline_backend_manager_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(CastBrowserMainParts);