Add installer_util_unittests to the GN windows build

chrome/app_installer/BUILD.gn

 # 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.
 
 import("//testing/test.gni")
 
 assert(is_win)
 
 executable("app_installer") {
   sources = [
-    "/win/app_installer_main.cc"
+    "win/app_installer_main.cc",
   ]
 
   configs -= [ "//build/config/win:console" ]
   configs += [ "//build/config/win:windowed" ]
 
   deps = [
     ":util",
     "//base",
   ]
 
@@ skipping 27 matching lines @@
   deps = [
     ":util",
     "//base",
     "//base/test:run_all_unittests",
     "//net:test_support",
     "//testing/gtest",
   ]
 
   # TODO(GYP) manifest
 }