[ObjC ARC] Converts ios/net to ARC.

ios/net/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.
 
 import("//ios/build/config.gni")
 import("//testing/test.gni")
 import("//url/features.gni")
 
 source_set("net") {
   deps = [
     "//base",
     "//net",
     "//url:url_features",
   ]
 
+  configs += [ "//build/config/compiler:enable_arc" ]
+
   sources = [
     "clients/crn_forwarding_network_client.h",
     "clients/crn_forwarding_network_client.mm",
     "clients/crn_forwarding_network_client_factory.h",
     "clients/crn_forwarding_network_client_factory.mm",
     "clients/crn_network_client_protocol.h",
     "clients/crn_simple_network_client_factory.h",
     "clients/crn_simple_network_client_factory.mm",
     "cookies/cookie_cache.cc",
     "cookies/cookie_cache.h",
@@ skipping 52 matching lines @@
     "cookies/cookie_store_ios_unittest.mm",
     "cookies/system_cookie_util_unittest.mm",
     "http_response_headers_util_unittest.mm",
     "nsurlrequest_util_unittest.mm",
     "protocol_handler_util_unittest.mm",
     "url_scheme_util_unittest.mm",
   ]
 
   assert_no_deps = ios_assert_no_deps
 }