[ObjC ARC] Converts ios/chrome/browser/ui/alert_coordinator:alert_coordinator_internal to ARC.

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") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "action_sheet_coordinator.h",
     "action_sheet_coordinator.mm",
     "alert_coordinator.h",
@@ skipping 31 matching lines @@
     "//ios/chrome/test:test_support",
     "//ios/web:test_support",
     "//testing/gtest",
     "//third_party/ocmock",
     "//ui/base",
     "//ui/strings",
   ]
 }
 
 source_set("alert_coordinator_internal") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "loading_alert_coordinator.h",
     "loading_alert_coordinator.mm",
   ]
   deps = [
     "//base",
     "//components/strings",
     "//ios/chrome/browser",
     "//ios/chrome/browser/ui",
     "//ios/chrome/browser/ui/material_components",
@@ skipping 16 matching lines @@
     "//components/strings",
     "//ios/chrome/test/earl_grey:test_support",
     "//ios/testing/earl_grey:earl_grey_support",
     "//ios/third_party/earl_grey",
   ]
   libs = [
     "UIKit.framework",
     "XCTest.framework",
   ]
 }