Convert spellcheck to a buildflag header.

build/config/features.gni

 # Copyright 2014 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.
 
 # =============================================
 #   PLEASE DO NOT ADD MORE FLAGS TO THIS FILE
 # =============================================
 #
 # These flags are effectively global. Your feature flag should go near the
 # code it controls. Most of these items are here now because they control
@@ skipping 70 matching lines @@
   # Enable WebVR support by default on Android
   # Still requires command line flag to access API
   # TODO(bshe): Enable for other architecture too. Currently we only support arm
   # and arm64.
   enable_webvr = is_android && is_component_build &&
                  (current_cpu == "arm" || current_cpu == "arm64")
 }
 
 # Additional dependent variables -----------------------------------------------
 
-# Enable the spell checker.
-enable_spellcheck = !is_ios
-
-# Use the operating system's spellchecker rather than hunspell.
-use_browser_spellchecker = is_android || is_mac
-
 # The seccomp-bpf sandbox is only supported on five architectures
 # currently.
 # Do not disable seccomp_bpf anywhere without talking to
 # security@chromium.org!
 use_seccomp_bpf =
     (is_linux || is_android) &&
     (current_cpu == "x86" || current_cpu == "x64" || current_cpu == "arm" ||
      current_cpu == "arm64" || current_cpu == "mipsel")
 
 # Enable notifications everywhere except iOS.
@@ skipping 16 matching lines @@
 
 enable_configuration_policy = !is_ios
 
 enable_mac_keystone = is_mac && is_chrome_branded && is_official_build
 #
 # =============================================
 #   PLEASE DO NOT ADD MORE FLAGS TO THIS FILE
 # =============================================
 #
 # See comment at the top.