[ObjC ARC] Converts ios/chrome/browser/browser_state to ARC.

ios/chrome/browser/browser_state/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.
 
 source_set("browser_state") {
   sources = [
     "browser_state_otr_helper.cc",
     "browser_state_otr_helper.h",
     "chrome_browser_state.h",
     "chrome_browser_state.mm",
   ]
   deps = [
     "//base",
     "//components/prefs",
     "//components/sync_preferences",
     "//ios/web",
     "//net",
   ]
+
+  configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 source_set("browser_state_impl") {
   sources = [
     "bookmark_model_loaded_observer.cc",
     "bookmark_model_loaded_observer.h",
     "browser_state_info_cache.cc",
     "browser_state_info_cache.h",
     "browser_state_info_cache_observer.h",
     "browser_state_keyed_service_factories.h",
@@ skipping 111 matching lines @@
     "//ios/chrome/browser/history",
     "//ios/chrome/browser/net",
     "//ios/chrome/browser/prefs",
     "//ios/chrome/browser/sync/glue",
     "//ios/chrome/test:test_support",
     "//ios/public/provider/chrome/browser",
     "//ios/web",
     "//net:test_support",
   ]
 }