[ObjC ARC] Converts ios/chrome/browser/ui/ntp:ntp_header to ARC.

ios/chrome/browser/ui/ntp/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.
 
 bundle_data("resources") {
   sources = [
     "resources/bookmarks_bar_bg.png",
     "resources/bookmarks_bar_bg@2x.png",
     "resources/bookmarks_bar_bg@2x~ipad.png",
     "resources/bookmarks_bar_bg_pressed@2x~ipad.png",
@@ skipping 92 matching lines @@
   ]
 }
 
 source_set("ntp") {
   sources = [
     "new_tab_page_panel_protocol.h",
   ]
 }
 
 source_set("ntp_header") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "google_landing_data_source.h",
     "new_tab_page_header_constants.h",
     "new_tab_page_header_constants.mm",
     "new_tab_page_header_view.h",
     "new_tab_page_header_view.mm",
     "new_tab_page_toolbar_controller.h",
     "new_tab_page_toolbar_controller.mm",
   ]
   deps = [
@@ skipping 181 matching lines @@
     "new_tab_page_perftest.mm",
   ]
   deps = [
     "//base/test:test_support",
     "//ios/chrome/browser/sessions",
     "//ios/chrome/browser/tabs",
     "//ios/chrome/browser/test:perf_test_support",
     "//ios/chrome/browser/ui:ui_internal",
   ]
 }