Add Mojo constant for "ash" and replace hardcoded strings

ash/mus/app_launch_unittest.cc

Index: ash/mus/app_launch_unittest.cc
diff --git a/ash/mus/app_launch_unittest.cc b/ash/mus/app_launch_unittest.cc
index 7cf67d04777f9bd7ec45c3afa073d95f5c47f470..1ee880a4cd046ed73ef02a8e5978b7f25d95f3aa 100644
--- a/ash/mus/app_launch_unittest.cc
+++ b/ash/mus/app_launch_unittest.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "ash/public/interfaces/constants.mojom.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/run_loop.h"
@@ -33,7 +34,7 @@ class AppLaunchTest : public service_manager::test::ServiceTest {
 };
 
 TEST_F(AppLaunchTest, TestQuickLaunch) {
-  connector()->Connect("ash");
+  connector()->Connect(mojom::kServiceName);
   connector()->Connect(mash::quick_launch::mojom::kServiceName);
 
   ui::mojom::WindowServerTestPtr test_interface;