[ObjC ARC] Converts ios/chrome/app/application_delegate:unit_tests to ARC.

ios/chrome/app/application_delegate/BUILD.gn

 # 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.
 
 source_set("application_delegate") {
   sources = [
     "memory_warning_helper.h",
     "memory_warning_helper.mm",
   ]
   deps = [
     "//base",
     "//ios/chrome/browser/crash_report",
     "//ios/chrome/browser/metrics",
   ]
   libs = [ "Foundation.framework" ]
 
   configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "app_state_unittest.mm",
     "background_activity_unittest.mm",
     "memory_warning_helper_unittest.mm",
     "metrics_mediator_unittest.mm",
     "url_opener_unittest.mm",
     "user_activity_handler_unittest.mm",
   ]
   deps = [
@@ skipping 115 matching lines @@
     "//base",
     "//base/test:test_support",
     "//ios/chrome/app:app_internal",
     "//ios/chrome/browser",
     "//net",
     "//ui/base",
     "//url",
   ]
   libs = [ "UIKit.framework" ]
 }