Convert spellcheck to a buildflag header.

chrome/browser/renderer_context_menu/spelling_menu_observer.cc

Index: chrome/browser/renderer_context_menu/spelling_menu_observer.cc
diff --git a/chrome/browser/renderer_context_menu/spelling_menu_observer.cc b/chrome/browser/renderer_context_menu/spelling_menu_observer.cc
index 0cbdbc707befd72eb671b984b7b66537ced76370..ca6f1d20efc6fbd8e3cc378b0d0bba5213fa78cb 100644
--- a/chrome/browser/renderer_context_menu/spelling_menu_observer.cc
+++ b/chrome/browser/renderer_context_menu/spelling_menu_observer.cc
@@ -28,6 +28,7 @@
 #include "components/spellcheck/browser/spelling_service_client.h"
 #include "components/spellcheck/common/spellcheck_common.h"
 #include "components/spellcheck/common/spellcheck_result.h"
+#include "components/spellcheck/spellcheck_build_features.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_view.h"
@@ -271,7 +272,7 @@ void SpellingMenuObserver::ExecuteCommand(int command_id) {
         spellcheck->GetFeedbackSender()->AddedToDictionary(misspelling_hash_);
       }
     }
-#if defined(USE_BROWSER_SPELLCHECKER)
+#if BUILDFLAG(USE_BROWSER_SPELLCHECKER)
     spellcheck_platform::AddWord(misspelled_word_);
 #endif
   }