Reland of GN: Enable ARC for Mac and iOS in rtc_* templates

webrtc/test/BUILD.gn

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("../webrtc.gni")
 import("//build/config/ui.gni")
@@ skipping 110 matching lines @@
 }
 
 rtc_source_set("fileutils") {
   testonly = true
   sources = [
     "testsupport/fileutils.cc",
     "testsupport/fileutils.h",
   ]
   if (is_ios) {
     sources += [ "testsupport/iosfileutils.mm" ]
-    configs += [ "//build/config/compiler:enable_arc" ]
   }
   visibility = [ ":*" ]
   deps = [
     "..:webrtc_common",
     "../base:rtc_base_approved",
   ]
   if (is_ios) {
     deps += [ "../sdk:rtc_sdk_common_objc" ]
   }
   if (is_win) {
@@ skipping 404 matching lines @@
     "mock_audio_decoder.h",
     "mock_audio_decoder_factory.h",
   ]
   deps = [
     ":test_support",
     "../api/audio_codecs:audio_codecs_api",
     "../api/audio_codecs:builtin_audio_decoder_factory",
     "../base:rtc_base_approved",
   ]
 }