Convert RLZ to a buildflag header

ios/chrome/browser/search_engines/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("//build/config/features.gni")
+import("//rlz/features/features.gni")
 
 source_set("search_engines") {
   sources = [
     "search_engines_util.cc",
     "search_engines_util.h",
     "template_url_service_client_impl.cc",
     "template_url_service_client_impl.h",
     "template_url_service_factory.cc",
     "template_url_service_factory.h",
     "ui_thread_search_terms_data.cc",
@@ skipping 10 matching lines @@
     "//components/search",
     "//components/search_engines",
     "//components/version_info",
     "//ios/chrome/browser",
     "//ios/chrome/browser/browser_state",
     "//ios/chrome/browser/google",
     "//ios/chrome/browser/history",
     "//ios/chrome/common",
     "//ios/web",
     "//net",
+    "//rlz/features",
     "//ui/base",
     "//url",
   ]
 
   if (enable_rlz) {
     deps += [ "//components/rlz" ]
   }
 }