Quit the message loop by default in ShellConnectionLost when ApplicationRunner is used

ash/mus/sysui_application.cc

Index: ash/mus/sysui_application.cc
diff --git a/ash/mus/sysui_application.cc b/ash/mus/sysui_application.cc
index 15a518612c845e3ed3cdc7b9a57b26678c722528..16585a31d4abb7d0c51b6f52f9f233df224449e6 100644
--- a/ash/mus/sysui_application.cc
+++ b/ash/mus/sysui_application.cc
@@ -16,7 +16,6 @@
 #include "ash/shell_window_ids.h"
 #include "base/bind.h"
 #include "base/files/file_path.h"
-#include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "components/mus/public/cpp/property_type_converters.h"
@@ -289,9 +288,5 @@ bool SysUIApplication::AcceptConnection(mojo::Connection* connection) {
   return true;
 }
 
-void SysUIApplication::ShellConnectionLost() {
-  base::MessageLoop::current()->QuitWhenIdle();
-}
-
 }  // namespace sysui
 }  // namespace ash