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

ios/chrome/browser/ui/authentication/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.
 
 import("//build/config/chrome_build.gni")
 
 bundle_data("resources") {
   sources = [
     "resources/signin_confirmation_more.png",
     "resources/signin_confirmation_more@2x.png",
@@ skipping 14 matching lines @@
       "resources/signin_promo_logo_chromium_color@2x.png",
       "resources/signin_promo_logo_chromium_color@3x.png",
     ]
   }
   outputs = [
     "{{bundle_resources_dir}}/{{source_file_part}}",
   ]
 }
 
 source_set("authentication") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "authentication_flow.h",
     "authentication_flow.mm",
     "authentication_flow_performer.h",
     "authentication_flow_performer.mm",
     "authentication_flow_performer_delegate.h",
     "authentication_ui_util.h",
     "authentication_ui_util.mm",
     "chrome_signin_view_controller.h",
     "chrome_signin_view_controller.mm",
@@ skipping 163 matching lines @@
     "//ios/chrome/browser/ui/tools_menu",
     "//ios/chrome/test/app:test_support",
     "//ios/chrome/test/earl_grey:test_support",
     "//ios/public/provider/chrome/browser/signin:test_support",
     "//ios/testing:ios_test_support",
     "//ios/testing/earl_grey:earl_grey_support",
     "//ios/third_party/earl_grey",
   ]
   libs = [ "XCTest.framework" ]
 }