### Preflight Checklist

* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

It would appear that `app.focus()` stopped working in Electron 6, and remains broken in Electron 8.

* **Electron Version:**
  * 8.0.3
* **Operating System:**
  * macOS
* **Last Known Working Electron version:**
  * 5.0.13

### Expected Behavior
`app.focus()` should bring the application to the foreground.

### Actual Behavior
`app.focus()` does nothing.

### To Reproduce

Fiddle: https://gist.github.com/a772265b312329e3f3bc1feb7b6aff7d

1) Start this fiddle.
2) As soon as the window pops up, select another application so that Electron is in the background.
3) Within 5 seconds, the app will attempt to focus itself to no avail.

shell/browser/browser_linux.cc
#include "shell/browser/browser.h"
#include <fcntl.h>
#include <stdlib.h>
#include "base/command_line.h"
#include "base/environment.h"
#include "base/process/launch.h"
#include "electron/electron_version.h"
#include "shell/browser/native_window.h"
#include "shell/browser/window_list.h"
#include "shell/common/application_info.h"
#if defined(USE_X11)
#include "chrome/browser/ui/gtk/gtk_util.h"
#include "shell/browser/linux/unity_service.h"
#endif
namespace electron {
const char kXdgSettings[] = "xdg-settings";
const char kXdgSettingsDefaultSchemeHandler[] = "default-url-scheme-handler";
class LaunchXdgUtilityScopedAllowBaseSyncPrimitives