Move enable extensions define to a build flag.

chrome/browser/renderer_host/chrome_render_message_filter.h

Index: chrome/browser/renderer_host/chrome_render_message_filter.h
diff --git a/chrome/browser/renderer_host/chrome_render_message_filter.h b/chrome/browser/renderer_host/chrome_render_message_filter.h
index 171e6c85f6c453509780725dc6c152c18084c406..afb9538a0af45ad90b8de0ec0a22bb7baae38298 100644
--- a/chrome/browser/renderer_host/chrome_render_message_filter.h
+++ b/chrome/browser/renderer_host/chrome_render_message_filter.h
@@ -12,6 +12,7 @@
 #include "base/macros.h"
 #include "base/sequenced_task_runner_helpers.h"
 #include "content/public/browser/browser_message_filter.h"
+#include "extensions/features/features.h"
 
 class GURL;
 class Profile;
@@ -84,7 +85,7 @@ class ChromeRenderMessageFilter : public content::BrowserMessageFilter {
                                      const GURL& origin_url,
                                      const GURL& top_origin_url,
                                      IPC::Message* message);
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   static void FileSystemAccessedSyncOnUIThread(
       int render_process_id,
       int render_frame_id,
@@ -105,7 +106,7 @@ class ChromeRenderMessageFilter : public content::BrowserMessageFilter {
                                  const GURL& origin_url,
                                  const GURL& top_origin_url,
                                  base::Callback<void(bool)> callback);
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   static void FileSystemAccessedOnUIThread(int render_process_id,
                                            int render_frame_id,
                                            const GURL& url,