[cast_channel] Make CastSocketService a global leaky singleton

chrome/browser/media/router/discovery/mdns/cast_media_sink_service.h

Index: chrome/browser/media/router/discovery/mdns/cast_media_sink_service.h
diff --git a/chrome/browser/media/router/discovery/mdns/cast_media_sink_service.h b/chrome/browser/media/router/discovery/mdns/cast_media_sink_service.h
index 2030c055fb8ae148ab6724d52968c79c34f86a9f..df6e60ebef2fde0c425a8dc8efa05d1fc4dfff88 100644
--- a/chrome/browser/media/router/discovery/mdns/cast_media_sink_service.h
+++ b/chrome/browser/media/router/discovery/mdns/cast_media_sink_service.h
@@ -16,6 +16,7 @@
 #include "chrome/browser/media/router/discovery/media_sink_service_base.h"
 #include "components/cast_channel/cast_channel_enum.h"
 #include "components/cast_channel/cast_socket.h"
+#include "content/public/browser/browser_thread.h"
 #include "net/base/ip_endpoint.h"
 
 namespace cast_channel {
@@ -119,8 +120,13 @@ class CastMediaSinkService
   // Service list from current round of discovery.
   DnsSdRegistry::DnsSdServiceList current_services_;
 
-  // Service managing creating and removing cast channels.
-  scoped_refptr<cast_channel::CastSocketService> cast_socket_service_;
+  // Raw pointer of leaky singleton CastSocketService, which manages creating
+  // and removing Cast sockets.
+  cast_channel::CastSocketService* const cast_socket_service_;
+
+  std::unique_ptr<cast_channel::CastSocket::Observer,
+                  content::BrowserThread::DeleteOnIOThread>
+      observer_;
 
   THREAD_CHECKER(thread_checker_);