Add service name constant for UI service.

ash/mus/accessibility_delegate_mus.cc

Index: ash/mus/accessibility_delegate_mus.cc
diff --git a/ash/mus/accessibility_delegate_mus.cc b/ash/mus/accessibility_delegate_mus.cc
index 1462507791ac26bc46ff04cbc9042a1e821aae9e..08e7ece102ed3ac346aba6b5453620b9f4718e6d 100644
--- a/ash/mus/accessibility_delegate_mus.cc
+++ b/ash/mus/accessibility_delegate_mus.cc
@@ -5,6 +5,7 @@
 #include "ash/mus/accessibility_delegate_mus.h"
 
 #include "services/service_manager/public/cpp/connector.h"
+#include "services/ui/public/interfaces/constants.mojom.h"
 
 namespace ash {
 
@@ -16,8 +17,10 @@ AccessibilityDelegateMus::~AccessibilityDelegateMus() {}
 
 ui::mojom::AccessibilityManager*
 AccessibilityDelegateMus::GetAccessibilityManager() {
-  if (!accessibility_manager_ptr_.is_bound())
-    connector_->ConnectToInterface("ui", &accessibility_manager_ptr_);
+  if (!accessibility_manager_ptr_.is_bound()) {
+    connector_->ConnectToInterface(ui::mojom::kServiceName,
+                                   &accessibility_manager_ptr_);
+  }
   return accessibility_manager_ptr_.get();
 }