Move enable extensions define to a build flag.

chrome/browser/interstitials/chrome_metrics_helper.h

Index: chrome/browser/interstitials/chrome_metrics_helper.h
diff --git a/chrome/browser/interstitials/chrome_metrics_helper.h b/chrome/browser/interstitials/chrome_metrics_helper.h
index 15736ded329ffb1cf31020d612fdba84007e3d11..f4a7b91dc2fa5d3f0d14946622e5da070488dfa0 100644
--- a/chrome/browser/interstitials/chrome_metrics_helper.h
+++ b/chrome/browser/interstitials/chrome_metrics_helper.h
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "chrome/common/features.h"
 #include "components/security_interstitials/core/metrics_helper.h"
+#include "extensions/features/features.h"
 #include "url/gurl.h"
 
 namespace content {
@@ -47,12 +48,12 @@ class ChromeMetricsHelper : public security_interstitials::MetricsHelper {
   void RecordExtraShutdownMetrics() override;
 
  private:
-#if BUILDFLAG(ENABLE_CAPTIVE_PORTAL_DETECTION) || defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_CAPTIVE_PORTAL_DETECTION) || BUILDFLAG(ENABLE_EXTENSIONS)
   content::WebContents* web_contents_;
 #endif
   const GURL request_url_;
   const std::string sampling_event_name_;
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   std::unique_ptr<extensions::ExperienceSamplingEvent> sampling_event_;
 #endif
 #if BUILDFLAG(ENABLE_CAPTIVE_PORTAL_DETECTION)