### 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
gin_helper::Arguments* args) {
  std::unique_ptr<base::Environment> env(base::Environment::Create());
  if (protocol.empty())
    return false;
  std::string desktop_name;
  if (!env->GetVar("CHROME_DESKTOP", &desktop_name))
    return false;
  const std::vector<std::string> argv = {kXdgSettings, "check",
                                         kXdgSettingsDefaultSchemeHandler,
                                         protocol, desktop_name};
  const auto output = GetXdgAppOutput(argv);
  if (!output)
    return false;
  
  return base::StartsWith(output.value(), "yes", base::CompareCase::SENSITIVE);
}
bool Browser::RemoveAsDefaultProtocolClient(const std::string& protocol,
                                            gin_helper::Arguments* args) {
  return false;
}
base::string16 Browser::GetApplicationNameForProtocol(const GURL& url) {
  const std::vector<std::string> argv = {
      "xdg-mime", "query", "default",
      std::string("x-scheme-handler/") + url.scheme()};
  return base::ASCIIToUTF16(GetXdgAppOutput(argv).value_or(std::string()));
}
bool Browser::SetBadgeCount(int count) {