Add service name constant for UI service.

mash/init/init.cc

Index: mash/init/init.cc
diff --git a/mash/init/init.cc b/mash/init/init.cc
index 09a1ca387f09faab4d247698fafcccad88b05ed6..0194457955729ea9662a3ff9fe48aeca826aa119 100644
--- a/mash/init/init.cc
+++ b/mash/init/init.cc
@@ -12,6 +12,7 @@
 #include "services/service_manager/public/cpp/connector.h"
 #include "services/service_manager/public/cpp/interface_registry.h"
 #include "services/service_manager/public/cpp/service_context.h"
+#include "services/ui/public/interfaces/constants.mojom.h"
 
 namespace mash {
 namespace init {
@@ -20,7 +21,7 @@ Init::Init() {}
 Init::~Init() {}
 
 void Init::OnStart() {
-  context()->connector()->Connect("ui");
+  context()->connector()->Connect(ui::mojom::kServiceName);
   StartTracing();
   StartLogin();
 }