Move enable extensions define to a build flag.

chrome/browser/download/download_target_determiner.cc

Index: chrome/browser/download/download_target_determiner.cc
diff --git a/chrome/browser/download/download_target_determiner.cc b/chrome/browser/download/download_target_determiner.cc
index b3841d70bb7eaae3d542a3a9c7f8a35be23c1f14..e1e662e79d7648e95e7b80725ece47ecedd6d5fe 100644
--- a/chrome/browser/download/download_target_determiner.cc
+++ b/chrome/browser/download/download_target_determiner.cc
@@ -26,11 +26,12 @@
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/download_interrupt_reasons.h"
 #include "extensions/common/constants.h"
+#include "extensions/features/features.h"
 #include "net/base/filename_util.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "url/origin.h"
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "chrome/browser/extensions/webstore_installer.h"
 #include "extensions/common/feature_switch.h"
 #endif
@@ -875,7 +876,7 @@ DownloadFileType::DangerLevel DownloadTargetDeterminer::GetDangerLevel(
     return DownloadFileType::NOT_DANGEROUS;
   }
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   // Extensions that are not from the gallery are considered dangerous.
   // When off-store install is disabled we skip this, since in this case, we
   // will not offer to install the extension.