Move enable extensions define to a build flag.

chrome/browser/plugins/plugin_info_message_filter.h

Index: chrome/browser/plugins/plugin_info_message_filter.h
diff --git a/chrome/browser/plugins/plugin_info_message_filter.h b/chrome/browser/plugins/plugin_info_message_filter.h
index 3c3506b526877cf2edfb0f216fe3ebd7146475be..057c7ed2ba4f9db174bf046e327e895bae1ad848 100644
--- a/chrome/browser/plugins/plugin_info_message_filter.h
+++ b/chrome/browser/plugins/plugin_info_message_filter.h
@@ -18,6 +18,7 @@
 #include "components/content_settings/core/common/content_settings.h"
 #include "components/prefs/pref_member.h"
 #include "content/public/browser/browser_message_filter.h"
+#include "extensions/features/features.h"
 #include "ppapi/features/features.h"
 
 struct ChromeViewHostMsg_GetPluginInfo_Output;
@@ -82,7 +83,7 @@ class PluginInfoMessageFilter : public content::BrowserMessageFilter {
    private:
     int render_process_id_;
     content::ResourceContext* resource_context_;
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
     extensions::ExtensionRegistry* extension_registry_;
 #endif
     const HostContentSettingsMap* host_content_settings_map_;