[ObjC ARC] Converts ios/public/provider/chrome/browser/voice:test_support to ARC.

ios/public/provider/chrome/browser/voice/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("voice") {
   sources = [
     "audio_session_controller.h",
     "logo_animation_controller.h",
     "voice_search_bar.h",
     "voice_search_bar_owner.h",
     "voice_search_controller.h",
     "voice_search_controller.mm",
     "voice_search_controller_delegate.h",
     "voice_search_language.h",
     "voice_search_language.mm",
     "voice_search_prefs.cc",
     "voice_search_prefs.h",
     "voice_search_presenter.h",
     "voice_search_provider.h",
     "voice_search_provider.mm",
   ]
   deps = [
     "//base",
   ]
 }
 
 source_set("test_support") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "test_audio_session_controller.cc",
     "test_audio_session_controller.h",
     "test_voice_search_provider.h",
     "test_voice_search_provider.mm",
   ]
 
   deps = [
     ":voice",
     "//base",
     "//ios/public/provider/chrome/browser",
   ]
 }