Move enable extensions define to a build flag.

chrome/renderer/chrome_mock_render_thread.h

Index: chrome/renderer/chrome_mock_render_thread.h
diff --git a/chrome/renderer/chrome_mock_render_thread.h b/chrome/renderer/chrome_mock_render_thread.h
index bc7901e4c8815345c2cfd05f29908a707a3689db..a7e01c24a9512acf4b5b8f005232627dec15e9e0 100644
--- a/chrome/renderer/chrome_mock_render_thread.h
+++ b/chrome/renderer/chrome_mock_render_thread.h
@@ -9,6 +9,7 @@
 
 #include "base/macros.h"
 #include "content/public/test/mock_render_thread.h"
+#include "extensions/features/features.h"
 
 struct ExtensionMsg_ExternalConnectionInfo;
 
@@ -33,7 +34,7 @@ class ChromeMockRenderThread : public content::MockRenderThread {
   bool OnMessageReceived(const IPC::Message& msg) override;
 
  private:
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   // The callee expects to be returned a valid channel_id.
   void OnOpenChannelToExtension(int routing_id,
                                 const ExtensionMsg_ExternalConnectionInfo& info,