I installed the latest version of Ubuntu (17.10) , but the problem is, I can't find the menu bars of applications in the GNOME panel. For instance, the Chrome menu bar doesn't appear on the panel like in Ubuntu 17.04 and earlier versions.
You may try a GNOME shell extension called "Gnome Global Application Menu(HUD for Gnome)". It provides a global application menu (i.e. menu bar of an application window in the top bar) à la Unity's global menu.
For detailed info you may visit the extension's GitHub page.
Warning: Performance may not be as smooth as Unity's global menu. See this if you want to deactivate/uninstall the extension correctly.
Current status and future of the extension
It will work for the next 6 month at less, as i'm waiting for the release of ubuntu 18.04 to take a desition of what i will do. If the default session of ubuntu 18.04 will be xorg i will continue with the extension for 6 month more. Also, if ubuntu or gnome developers fix or help to fix unity-gtk-module in wayland i will continue the extension. What i will not do is continues making improvements, because this have not sense if will not work on Wayland. Also if the ubuntu developers want to implemented it i will donate the extension to hims and i will help in what is needed. - the developer, 27 Oct 2017
Update: The extension has been discontinued by its original developer. Please consider not using this extension.
Ubuntu is now using GNOME as a primary desktop and then they are following up the GNOME Human Interface Guidelines (HIG). In GNOME they concidered rigth now the menubar an inferior solution:
Menu bars increase the vertical footprint of an application’s user interface, introduce a large number of disclosure points, and function as a fixed set of inflexible options. For these reasons, header bars and header bar menus are generally recommended over menu bars, along with other design patterns for exposing controls on demand, such as selection mode, action bars, and popovers.
A global menu is a menubar exported in a service (a DBUS service). So, to have a global menu, as you are wishing, you need to have a menubar or an internal representation of it at less. But most of GNOME core applications have not a menubar right now. The Ubuntu developers were working on include a menubar to the GNOME core applications some years ago, but they abandon that project at same time they were abandon Unity:
As this Ubuntu project existed, a GNOME shell extension called "Gnome Global Application Menu(HUD for Gnome)" was created. But when the ubuntu developers decided to not support the project, the extension stopped making sense.
So, is not possible to have again a global menu in Ubuntu with GNOME, unless the project of the Ubuntu developers come again to the live, we find a way to hack the GNOME core applications or the GNOME designers and developers change his mind about this feature in the future.
Of course we can select an alternative desktop environment in Ubuntu where the core applications of this desktop have a menubar and then the desktop can implement a global menu for it. This can be for example KDE, Mate and more but currently not GNOME.
Like others things more, not have a menubar is a humman desicion, not an impossibility of the GNOME desktop or the GNOME applications, but the result is that finally you can not have a global menu in a concistent way in GNOME.