[ObjC ARC] Converts ios/chrome/common to ARC

ios/chrome/common/BUILD.gn

 # Copyright 2015 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("common") {
   sources = [
     "channel_info.h",
     "channel_info.mm",
     "material_timing.h",
     "material_timing.mm",
     "string_util.h",
     "string_util.mm",
     "x_callback_url.cc",
     "x_callback_url.h",
   ]
 
+  configs += [ "//build/config/compiler:enable_arc" ]
+
   deps = [
     "//base",
     "//components/version_info",
     "//ios/chrome/common/app_group:main_app",
     "//ios/chrome/common/physical_web:physical_web",
     "//net",
     "//url",
   ]
 
   libs = [ "QuartzCore.framework" ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "string_util_unittest.mm",
     "x_callback_url_unittest.cc",
   ]
   deps = [
     ":common",
     "//base",
     "//testing/gtest",
   ]
 }