[ObjC ARC] Converts ios/web:ios_web_webui_unittests to ARC.

ios/web/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("//ios/web/js_compile.gni")
 import("//testing/test.gni")
 import("//tools/grit/grit_rule.gni")
 
 group("all_tests") {
@@ skipping 717 matching lines @@
     "web_state/ui/crw_web_view_scroll_view_proxy_unittest.mm",
     "web_state/ui/crw_wk_navigation_states_unittest.mm",
     "web_state/ui/crw_wk_script_message_router_unittest.mm",
     "web_state/ui/web_view_js_utils_unittest.mm",
     "web_state/ui/wk_back_forward_list_item_holder_unittest.mm",
     "web_state/ui/wk_web_view_configuration_provider_unittest.mm",
   ]
 }
 
 source_set("ios_web_webui_unittests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   deps = [
     ":core",
     ":user_agent",
     ":web",
     "//base",
     "//base/test:test_support",
     "//components/payments/core",
     "//components/url_formatter",
     "//ios/net",
@@ skipping 108 matching lines @@
     "ios_web_resources.pak",
   ]
   grit_flags = [
     "-E",
     "root_gen_dir=" + rebase_path(root_gen_dir, root_build_dir),
   ]
   deps = [
     "//mojo/public/js:bindings",
   ]
 }