Reland of [ObjC ARC] Converts ios/chrome/browser/ui/contextual_search:contextual_search 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 14 matching lines @@
   testonly = true
   sources = [
     "resources/contextualsearch_unittest.js",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_file_part}}",
   ]
 }
 
 source_set("contextual_search") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "contextual_search_context.cc",
     "contextual_search_context.h",
     "contextual_search_controller.h",
     "contextual_search_controller.mm",
     "contextual_search_delegate.cc",
     "contextual_search_delegate.h",
     "contextual_search_header_view.h",
     "contextual_search_header_view.mm",
     "contextual_search_highlighter_view.h",
@@ skipping 89 matching lines @@
     "//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",
   ]
 }