Convert spellcheck to a buildflag header.

android_webview/BUILD.gn

 # Copyright 2015 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("//android_webview/system_webview_apk_tmpl.gni")
+import("//android_webview/webview_repack_locales.gni")
 import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
 import("//build/config/locales.gni")
+import("//components/spellcheck/spellcheck_build_features.gni")
 import("//tools/grit/repack.gni")
 import("//tools/resources/generate_resource_whitelist.gni")
-import("system_webview_apk_tmpl.gni")
-import("webview_repack_locales.gni")
 
 declare_args() {
   # Package name of the system_webview_apk target.
   system_webview_package_name = "com.android.webview"
 }
 
 if (!defined(use_webview_internal_framework)) {
   use_webview_internal_framework = false
 }
 
@@ skipping 459 matching lines @@
     "//components/metrics",
     "//components/metrics:gpu",
     "//components/metrics:net",
     "//components/metrics:profiler",
     "//components/metrics:ui",
     "//components/navigation_interception",
     "//components/prefs",
     "//components/printing/browser",
     "//components/printing/common",
     "//components/printing/renderer",
+    "//components/spellcheck:build_features",
     "//components/supervised_user_error_page",
     "//components/supervised_user_error_page:gin",
     "//components/version_info",
     "//components/visitedlink/browser",
     "//components/visitedlink/renderer",
     "//components/web_contents_delegate_android:web_contents_delegate_android",
     "//components/web_restrictions:browser",
     "//content",
     "//content/public/app:both",
     "//content/public/browser",
@@ skipping 183 matching lines @@
   system_webview_apk_tmpl("system_webview_apk") {
     android_manifest = system_webview_android_manifest
     android_manifest_dep = ":system_webview_manifest"
     deps = [
       ":system_webview_resources",
       "//android_webview/glue",
     ]
     apk_name = "SystemWebView"
   }
 }