Convert spellcheck to a buildflag header.

android_webview/renderer/aw_content_renderer_client.h

Index: android_webview/renderer/aw_content_renderer_client.h
diff --git a/android_webview/renderer/aw_content_renderer_client.h b/android_webview/renderer/aw_content_renderer_client.h
index ac0312c85045bccb747cebda8d49196bcce0274c..578a2e36da9c7540336307349e8d9ce8bf51e2dd 100644
--- a/android_webview/renderer/aw_content_renderer_client.h
+++ b/android_webview/renderer/aw_content_renderer_client.h
@@ -11,10 +11,11 @@
 #include "android_webview/renderer/aw_render_thread_observer.h"
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
+#include "components/spellcheck/spellcheck_build_features.h"
 #include "components/web_restrictions/interfaces/web_restrictions.mojom.h"
 #include "content/public/renderer/content_renderer_client.h"
 
-#if defined(ENABLE_SPELLCHECK)
+#if BUILDFLAG(ENABLE_SPELLCHECK)
 class SpellCheck;
 class SpellCheckProvider;
 #endif
@@ -62,7 +63,7 @@ class AwContentRendererClient : public content::ContentRendererClient {
   std::unique_ptr<visitedlink::VisitedLinkSlave> visited_link_slave_;
   web_restrictions::mojom::WebRestrictionsPtr web_restrictions_service_;
 
-#if defined(ENABLE_SPELLCHECK)
+#if BUILDFLAG(ENABLE_SPELLCHECK)
   std::unique_ptr<SpellCheck> spellcheck_;
 #endif