Move enable extensions define to a build flag.

chrome/browser/ui/login/login_handler.cc

Index: chrome/browser/ui/login/login_handler.cc
diff --git a/chrome/browser/ui/login/login_handler.cc b/chrome/browser/ui/login/login_handler.cc
index ad085a9c2db4e25271c6c98e4e06d8e48c22deaf..4382d75f1a74736b52afbb6d6d3e91488d3790ec 100644
--- a/chrome/browser/ui/login/login_handler.cc
+++ b/chrome/browser/ui/login/login_handler.cc
@@ -32,6 +32,7 @@
 #include "content/public/browser/resource_request_info.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/origin_util.h"
+#include "extensions/features/features.h"
 #include "net/base/auth.h"
 #include "net/base/host_port_pair.h"
 #include "net/base/load_flags.h"
@@ -43,7 +44,7 @@
 #include "ui/gfx/text_elider.h"
 #include "url/origin.h"
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "components/guest_view/browser/guest_view_base.h"
 #include "extensions/browser/view_type_utils.h"
 #endif
@@ -548,7 +549,7 @@ void LoginHandler::ShowLoginPrompt(const GURL& request_url,
       handler->GetPasswordManagerForLogin();
 
   if (!password_manager) {
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
     // A WebContents in a <webview> (a GuestView type) does not have a password
     // manager, but still needs to be able to show login prompts.
     const auto* guest =