Add service name constant for UI service.

ash/mus/accessibility_delegate_mus.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #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 {
 
 AccessibilityDelegateMus::AccessibilityDelegateMus(
     service_manager::Connector* connector)
     : connector_(connector) {}
 
 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();
 }
 
 void AccessibilityDelegateMus::ToggleHighContrast() {
   DefaultAccessibilityDelegate::ToggleHighContrast();
   GetAccessibilityManager()->SetHighContrastMode(IsHighContrastEnabled());
 }
 
 }  // namespace ash