Add Mojo constant for "ash" and replace hardcoded strings

ash/mus/window_manager_unittest.cc

 // Copyright 2015 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 <map>
 #include <memory>
 #include <vector>
 
+#include "ash/public/interfaces/constants.mojom.h"
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "services/service_manager/public/cpp/service_test.h"
 #include "services/ui/public/cpp/property_type_converters.h"
 #include "services/ui/public/interfaces/window_tree.mojom.h"
 #include "ui/aura/env.h"
 #include "ui/aura/mus/property_converter.h"
 #include "ui/aura/mus/window_tree_client.h"
 #include "ui/aura/mus/window_tree_client_delegate.h"
@@ skipping 57 matching lines @@
 
 TEST_F(WindowManagerTest, OpenWindow) {
   display::ScreenBase screen;
   screen.display_list().AddDisplay(
       display::Display(1, gfx::Rect(0, 0, 200, 200)),
       display::DisplayList::Type::PRIMARY);
   display::Screen::SetScreenInstance(&screen);
 
   WindowTreeClientDelegate window_tree_delegate;
 
-  connector()->Connect("ash");
+  connector()->Connect(mojom::kServiceName);
 
   // Connect to mus and create a new top level window. The request goes to
   // |ash|, but is async.
   aura::WindowTreeClient client(connector(), &window_tree_delegate);
   client.ConnectViaWindowTreeFactory();
   aura::test::EnvTestHelper().SetWindowTreeClient(&client);
   std::map<std::string, std::vector<uint8_t>> properties;
   properties[ui::mojom::WindowManager::kWindowType_InitProperty] =
       mojo::ConvertTo<std::vector<uint8_t>>(
           static_cast<int32_t>(ui::mojom::WindowType::WINDOW));
@@ skipping 10 matching lines @@
   client.Embed(child_window, std::move(tree_client), 0u, base::Bind(&OnEmbed));
   aura::WindowTreeClient child_client(connector(), &window_tree_delegate,
                                       nullptr, std::move(tree_client_request));
   window_tree_delegate.WaitForEmbed();
   ASSERT_TRUE(!child_client.GetRoots().empty());
   window_tree_delegate.DestroyWindowTreeHost();
 }
 
 }  // namespace mus
 }  // namespace ash