Move enable extensions define to a build flag.

chrome/common/pref_names.h

Index: chrome/common/pref_names.h
diff --git a/chrome/common/pref_names.h b/chrome/common/pref_names.h
index 36568586b73a33b4243e0e0b3cfb0184a0fbb896..ea495ff68ea2e05db0784957e819dbcef4fc5b6f 100644
--- a/chrome/common/pref_names.h
+++ b/chrome/common/pref_names.h
@@ -11,6 +11,7 @@
 
 #include "build/build_config.h"
 #include "chrome/common/features.h"
+#include "extensions/features/features.h"
 
 namespace prefs {
 
@@ -433,7 +434,7 @@ extern const char kEasyUnlockEnabled[];
 extern const char kEasyUnlockPairing[];
 extern const char kEasyUnlockProximityRequired[];
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 extern const char kToolbarIconSurfacingBubbleAcknowledged[];
 extern const char kToolbarIconSurfacingBubbleLastShowTime[];
 extern const char kToolbarMigratedComponentActionStatus[];
@@ -817,7 +818,7 @@ extern const char kRegisteredSupervisedUserWhitelists[];
 extern const char kRestartInBackground[];
 #endif
 
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
 extern const char kAnimationPolicy[];
 #endif