Add service name constant for UI service.

ui/views/mus/screen_mus.cc

Index: ui/views/mus/screen_mus.cc
diff --git a/ui/views/mus/screen_mus.cc b/ui/views/mus/screen_mus.cc
index ce12f880cc79a99a9f8c65451c3237a3c0dfa361..d4bf861783fa14d7608ada4047ce265a203d3f26 100644
--- a/ui/views/mus/screen_mus.cc
+++ b/ui/views/mus/screen_mus.cc
@@ -10,6 +10,7 @@
 
 #include "services/service_manager/public/cpp/connection.h"
 #include "services/service_manager/public/cpp/connector.h"
+#include "services/ui/public/interfaces/constants.mojom.h"
 #include "ui/aura/window.h"
 #include "ui/views/mus/native_widget_mus.h"
 #include "ui/views/mus/screen_mus_delegate.h"
@@ -47,7 +48,7 @@ ScreenMus::~ScreenMus() {
 }
 
 void ScreenMus::Init(service_manager::Connector* connector) {
-  connector->ConnectToInterface("ui", &display_manager_);
+  connector->ConnectToInterface(ui::mojom::kServiceName, &display_manager_);
 
   display_manager_->AddObserver(
       display_manager_observer_binding_.CreateInterfacePtrAndBind());