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

ios/chrome/browser/ui/first_run/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("assets") {
   sources = [
     "resources/FirstRun.xcassets/checkbox.imageset/Contents.json",
     "resources/FirstRun.xcassets/checkbox.imageset/checkbox.png",
     "resources/FirstRun.xcassets/checkbox.imageset/checkbox@2x.png",
     "resources/FirstRun.xcassets/checkbox.imageset/checkbox@2x~ipad.png",
     "resources/FirstRun.xcassets/checkbox.imageset/checkbox@3x.png",
     "resources/FirstRun.xcassets/checkbox.imageset/checkbox~ipad.png",
     "resources/FirstRun.xcassets/checkbox_checked.imageset/Contents.json",
     "resources/FirstRun.xcassets/checkbox_checked.imageset/checkbox_checked.png",
     "resources/FirstRun.xcassets/checkbox_checked.imageset/checkbox_checked@2x.png",
     "resources/FirstRun.xcassets/checkbox_checked.imageset/checkbox_checked@2x~ipad.png",
     "resources/FirstRun.xcassets/checkbox_checked.imageset/checkbox_checked@3x.png",
     "resources/FirstRun.xcassets/checkbox_checked.imageset/checkbox_checked~ipad.png",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_file_part}}",
   ]
 }
 
 source_set("first_run") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "first_run_chrome_signin_view_controller.h",
     "first_run_chrome_signin_view_controller.mm",
     "first_run_histograms.h",
     "first_run_util.h",
     "first_run_util.mm",
     "static_file_view_controller.h",
     "static_file_view_controller.mm",
     "welcome_to_chrome_view.h",
     "welcome_to_chrome_view.mm",
@@ skipping 78 matching lines @@
     "//ios/chrome/browser/signin",
     "//ios/chrome/browser/sync",
     "//ios/chrome/test/app:test_support",
     "//ios/chrome/test/earl_grey:test_support",
     "//ios/public/provider/chrome/browser/signin:test_support",
     "//ios/third_party/earl_grey",
     "//ui/base",
   ]
   libs = [ "XCTest.framework" ]
 }