Pref service: add a factory to create the client lib

services/service_manager/public/tools/test/service_test.gni

 # Copyright 2017 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.
 
 import("//services/catalog/public/tools/catalog.gni")
 import("//testing/test.gni")
 
 # Generates a unittest binary with a baked-in Service Manager catalog manifest.
 #
 # Parameters:
@@ skipping 13 matching lines @@
     if (!defined(deps)) {
       deps = []
     }
     deps += [
       ":$catalog_source_target",
       "//services/service_manager/public/cpp/test:run_all_service_tests",
     ]
   }
 
   catalog_cpp_source(catalog_source_target) {
+    testonly = true
     catalog = invoker.catalog
     generated_function_name = "service_manager::test::CreateTestCatalog"
   }
 }