Add service name constant for UI service.

services/ui/demo/mus_demo_unittests.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 "base/bind.h"
 #include "base/command_line.h"
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "services/service_manager/public/cpp/service_test.h"
+#include "services/ui/public/interfaces/constants.mojom.h"
 #include "services/ui/public/interfaces/window_server_test.mojom.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace ui {
 namespace demo {
 
 namespace {
 
 const char kTestAppName[] = "mus_demo_unittests";
 
@@ skipping 15 matching lines @@
  private:
   DISALLOW_COPY_AND_ASSIGN(MusDemoTest);
 };
 
 }  // namespace
 
 TEST_F(MusDemoTest, CheckMusDemoDraws) {
   connector()->Connect("mus_demo");
 
   ::ui::mojom::WindowServerTestPtr test_interface;
-  connector()->ConnectToInterface("ui", &test_interface);
+  connector()->ConnectToInterface(ui::mojom::kServiceName, &test_interface);
 
   base::RunLoop run_loop;
   bool success = false;
   // TODO(kylechar): Fix WindowServer::CreateTreeForWindowManager so that the
   // WindowTree has the correct name instead of an empty name.
   test_interface->EnsureClientHasDrawnWindow(
       "",  // WindowTree name is empty.
       base::Bind(&RunCallback, &success, run_loop.QuitClosure()));
   run_loop.Run();
   EXPECT_TRUE(success);
 }
 
 }  // namespace demo
 }  // namespace ui