[ObjC ARC] Converts ios/chrome/today_extension:today_extension to ARC.

ios/chrome/today_extension/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/ios/rules.gni")
 import("//build/config/locales.gni")
 import("//build/config/mac/base_rules.gni")
 import("//build/mac/tweak_info_plist.gni")
 import("//ios/build/chrome_build.gni")
 import("//ios/chrome/extension_repack.gni")
@@ skipping 12 matching lines @@
 
 compile_plist("entitlements") {
   format = "xml1"
   substitutions = [ "IOS_BUNDLE_ID_PREFIX=$ios_app_bundle_id_prefix" ]
   output_name = "$target_gen_dir/today_extension.appex.entitlements"
   plist_templates =
       [ "entitlements/external/today_extension.appex.entitlements" ]
 }
 
 ios_appex_bundle("today_extension") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "footer_label.h",
     "footer_label.mm",
     "interactive_label.h",
     "interactive_label.mm",
     "lock_screen_state.h",
     "lock_screen_state.mm",
     "notification_center_button.h",
     "notification_center_button.mm",
     "notification_center_url_button.h",
@@ skipping 66 matching lines @@
     "resources/todayview_physical_web@2x.png",
     "resources/todayview_physical_web@3x.png",
     "resources/todayview_voice_search.png",
     "resources/todayview_voice_search@2x.png",
     "resources/todayview_voice_search@3x.png",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_file_part}}",
   ]
 }