Move enable extensions define to a build flag.

chrome/browser/ui/webui/constrained_web_dialog_ui.cc

Index: chrome/browser/ui/webui/constrained_web_dialog_ui.cc
diff --git a/chrome/browser/ui/webui/constrained_web_dialog_ui.cc b/chrome/browser/ui/webui/constrained_web_dialog_ui.cc
index 1b88b6c1a49edae262d5305bc394ac605159b478..7be906ffe60996559320730bd1fe78eae85abec4 100644
--- a/chrome/browser/ui/webui/constrained_web_dialog_ui.cc
+++ b/chrome/browser/ui/webui/constrained_web_dialog_ui.cc
@@ -16,10 +16,11 @@
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_ui.h"
+#include "extensions/features/features.h"
 #include "ui/web_dialogs/web_dialog_delegate.h"
 #include "ui/web_dialogs/web_dialog_ui.h"
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "chrome/browser/extensions/tab_helper.h"
 #endif
 
@@ -51,7 +52,7 @@ class ConstrainedWebDialogDelegateUserData
 
 ConstrainedWebDialogUI::ConstrainedWebDialogUI(content::WebUI* web_ui)
     : WebUIController(web_ui) {
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   extensions::TabHelper::CreateForWebContents(web_ui->GetWebContents());
 #endif
 }