Move enable extensions define to a build flag.

chrome/browser/download/download_history.cc

Index: chrome/browser/download/download_history.cc
diff --git a/chrome/browser/download/download_history.cc b/chrome/browser/download/download_history.cc
index 49262d0d42d9fca3591ac486b2b6a0d48e259efc..c472e7c112535870f0cacb482dce7ff11cae35af 100644
--- a/chrome/browser/download/download_history.cc
+++ b/chrome/browser/download/download_history.cc
@@ -40,8 +40,9 @@
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/download_item.h"
 #include "content/public/browser/download_manager.h"
+#include "extensions/features/features.h"
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "chrome/browser/extensions/api/downloads/downloads_api.h"
 #endif
 
@@ -117,7 +118,7 @@ const char DownloadHistoryData::kKey[] =
 history::DownloadRow GetDownloadRow(
     content::DownloadItem* item) {
   std::string by_ext_id, by_ext_name;
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   extensions::DownloadedByExtension* by_ext =
       extensions::DownloadedByExtension::Get(item);
   if (by_ext) {
@@ -275,7 +276,7 @@ void DownloadHistory::QueryCallback(std::unique_ptr<InfoVector> infos) {
         history::ToContentDownloadDangerType(it->danger_type),
         history::ToContentDownloadInterruptReason(it->interrupt_reason),
         it->opened);
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
     if (!it->by_ext_id.empty() && !it->by_ext_name.empty()) {
       new extensions::DownloadedByExtension(
           item, it->by_ext_id, it->by_ext_name);