[ObjC ARC] Converts ios/chrome/browser/ui/alert_coordinator:unit_tests to ARC.Automatically gener…

ios/chrome/browser/ui/alert_coordinator/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("alert_coordinator") {
   sources = [
     "action_sheet_coordinator.h",
     "action_sheet_coordinator.mm",
     "alert_coordinator.h",
     "alert_coordinator.mm",
     "input_alert_coordinator.h",
     "input_alert_coordinator.mm",
   ]
   deps = [
     "//base",
     "//ios/chrome/browser",
     "//ui/base",
     "//ui/strings",
   ]
 }
 
 source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "action_sheet_coordinator_unittest.mm",
     "alert_coordinator_unittest.mm",
     "input_alert_coordinator_unittest.mm",
   ]
   deps = [
     ":alert_coordinator",
     "//base",
     "//testing/gtest",
     "//third_party/ocmock",
     "//ui/base",
     "//ui/strings",
   ]
 }