[ObjC ARC] Converts ios/chrome/browser/ui/contextual_search:unit_tests to ARC.

ios/chrome/browser/ui/contextual_search/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.
 
 import("//ios/web/js_compile.gni")
 
 bundle_data("resources") {
   sources = [
     "resources/expand_less.png",
     "resources/expand_less@2x.png",
@@ skipping 98 matching lines @@
   sources = [
     "touch_to_search_permissions_mediator+testing.h",
     "touch_to_search_permissions_mediator+testing.mm",
   ]
   deps = [
     ":contextual_search",
   ]
 }
 
 source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "contextual_search_js_unittest.mm",
     "touch_to_search_permissions_mediator_unittest.mm",
   ]
   deps = [
     ":contextual_search",
     ":resources_unit_tests",
     ":test_support",
     "//base",
     "//base/test:test_support",
     "//components/pref_registry",
     "//components/prefs",
     "//components/search_engines",
     "//ios/chrome/browser",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/search_engines",
     "//ios/chrome/browser/sync",
     "//ios/chrome/browser/sync:test_support",
     "//ios/chrome/browser/web:test_support",
     "//ios/web",
     "//ios/web:test_support",
     "//net",
     "//testing/gtest",
     "//third_party/ocmock",
   ]
 }