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

mash/wm/window_manager_application.cc

Index: mash/wm/window_manager_application.cc
diff --git a/mash/wm/window_manager_application.cc b/mash/wm/window_manager_application.cc
index 606de459a7f58eb68e78961a85bbd2b297dc5a82..57fb884cc2d3062385317f055f398b3493523c1c 100644
--- a/mash/wm/window_manager_application.cc
+++ b/mash/wm/window_manager_application.cc
@@ -127,10 +127,6 @@ bool WindowManagerApplication::AcceptConnection(mojo::Connection* connection) {
   return true;
 }
 
-void WindowManagerApplication::ShellConnectionLost() {
-  _exit(1);
-}
-
 void WindowManagerApplication::Create(
     mojo::Connection* connection,
     mojo::InterfaceRequest<mash::wm::mojom::UserWindowController> request) {