[chromecast] Pass media task runner to MediaPipelineBackendManager.

chromecast/browser/cast_content_browser_client.h

Index: chromecast/browser/cast_content_browser_client.h
diff --git a/chromecast/browser/cast_content_browser_client.h b/chromecast/browser/cast_content_browser_client.h
index 19ccffacc522ab4e15ac669d140e9b70826791ca..5f0d77eab96d9a74092d0f2c82070b59b81961fe 100644
--- a/chromecast/browser/cast_content_browser_client.h
+++ b/chromecast/browser/cast_content_browser_client.h
@@ -33,6 +33,7 @@ class CastService;
 
 namespace media {
 class MediaPipelineBackend;
+class MediaPipelineBackendManager;
 struct MediaPipelineDeviceParams;
 class MediaResourceTracker;
 class VideoPlaneController;
@@ -73,6 +74,8 @@ class CastContentBrowserClient : public content::ContentBrowserClient {
       const media::MediaPipelineDeviceParams& params);
 
   media::MediaResourceTracker* media_resource_tracker();
+
+  media::MediaPipelineBackendManager* media_pipeline_backend_manager();
 #endif
 
   // Invoked when the metrics client ID changes.