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

ios/chrome/browser/ui/popup_menu/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.
 
 bundle_data("resources") {
   sources = [
     "resources/popup_background.png",
     "resources/popup_background@2x.png",
     "resources/popup_background@3x.png",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_file_part}}",
   ]
 }
 
 source_set("popup_menu") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "popup_menu_controller.h",
     "popup_menu_controller.mm",
     "popup_menu_view.h",
     "popup_menu_view.mm",
   ]
   deps = [
     ":resources",
     "//base",
     "//ios/chrome/app/strings",
     "//ios/chrome/browser/ui",
     "//ios/chrome/common",
     "//ui/base",
   ]
   libs = [
     "QuartzCore.framework",
     "UIKit.framework",
   ]
 }