Move enable extensions define to a build flag.

chrome/browser/ui/unload_controller.cc

Index: chrome/browser/ui/unload_controller.cc
diff --git a/chrome/browser/ui/unload_controller.cc b/chrome/browser/ui/unload_controller.cc
index 55bc8544c9236d6ef20da9d9b4a9bede93420537..8da59883131c958fbd7a16fe9daa400225b43eb7 100644
--- a/chrome/browser/ui/unload_controller.cc
+++ b/chrome/browser/ui/unload_controller.cc
@@ -17,8 +17,9 @@
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/web_contents.h"
+#include "extensions/features/features.h"
 
-#if defined (ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "extensions/browser/extension_registry.h"
 #include "extensions/common/constants.h"
 #endif  // (ENABLE_EXTENSIONS)
@@ -56,7 +57,7 @@ bool UnloadController::ShouldRunUnloadEventsHelper(
 }
 
 bool UnloadController::RunUnloadEventsHelper(content::WebContents* contents) {
-#if defined (ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   // Don't run for extensions that are disabled or uninstalled; the tabs will
   // be killed if they make any network requests, and the extension shouldn't
   // be doing any work if it's removed.