Do not rely on Constructor to call Init

This makes it deterministic when the JavaScript is initialized, which
can make our logic more clear.

atom/browser/api/atom_api_menu_mac.h

@@ -17,7 +17,7 @@ namespace api {
 
 class MenuMac : public Menu {
  protected:
-  explicit MenuMac(v8::Isolate* isolate);
+  MenuMac(v8::Isolate* isolate, v8::Local<v8::Object> wrapper);
 
   void PopupAt(Window* window, int x, int y, int positioning_item) override;