Convert spellcheck to a buildflag header.

android_webview/native/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("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
+import("//components/spellcheck/spellcheck_build_features.gni")
 
 source_set("native") {
   deps = [
     ":native_jni",
     "//android_webview/common:version",
     "//base",
     "//base/third_party/dynamic_annotations:dynamic_annotations",
     "//cc:cc",
     "//components/autofill/content/browser:browser",
+    "//components/spellcheck:build_features",
     "//components/strings",
     "//components/web_contents_delegate_android:web_contents_delegate_android",
     "//content/public/common",
     "//device/battery:mojo_bindings",
     "//media/base/android:android",
     "//net",
     "//skia",
     "//storage/browser",
     "//storage/common",
     "//third_party/boringssl",
@@ skipping 133 matching lines @@
 generate_jar_jni("cancellation_signal_android_jar_jni_headers") {
   classes = [ "android/os/CancellationSignal.class" ]
   jni_package = "android_webview"
 }
 
 java_cpp_enum("aw_permission_request_resource") {
   sources = [
     "permission/aw_permission_request.h",
   ]
 }