### 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
const std::vector<std::string>& argv) {
  std::string reply;
  int success_code;
  GetXdgAppOutputScopedAllowBlocking allow_blocking;
  bool ran_ok = base::GetAppOutputWithExitCode(base::CommandLine(argv), &reply,
                                               &success_code);
  if (!ran_ok || success_code != EXIT_SUCCESS)
    return base::Optional<std::string>();
  return base::make_optional(reply);
}
bool SetDefaultWebClient(const std::string& protocol) {
  std::unique_ptr<base::Environment> env(base::Environment::Create());
  std::vector<std::string> argv = {kXdgSettings, "set"};
  if (!protocol.empty()) {
    argv.emplace_back(kXdgSettingsDefaultSchemeHandler);
    argv.emplace_back(protocol);
  }
  std::string desktop_name;
  if (!env->GetVar("CHROME_DESKTOP", &desktop_name)) {
    return false;
  }
  argv.emplace_back(desktop_name);
  int exit_code;
  bool ran_ok = LaunchXdgUtility(argv, &exit_code);
  return ran_ok && exit_code == EXIT_SUCCESS;
}
void Browser::Focus() {