### 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_win.cc
const base::string16 url_scheme = base::ASCIIToUTF16(url.scheme());
  if (!IsValidCustomProtocol(url_scheme))
    return base::string16();
  
  base::string16 command_to_launch;
  base::win::RegKey cmd_key_name(HKEY_CLASSES_ROOT, url_scheme.c_str(),
                                 KEY_READ);
  if (cmd_key_name.ReadValue(NULL, &command_to_launch) == ERROR_SUCCESS &&
      !command_to_launch.empty()) {
    return command_to_launch;
  }
  
  
  const base::string16 cmd_key_path = url_scheme + L"\\shell\\open\\command";
  base::win::RegKey cmd_key_exe(HKEY_CLASSES_ROOT, cmd_key_path.c_str(),
                                KEY_READ);
  if (cmd_key_exe.ReadValue(NULL, &command_to_launch) == ERROR_SUCCESS) {
    base::CommandLine command_line(
        base::CommandLine::FromString(command_to_launch));
    return command_line.GetProgram().BaseName().value();
  }
  return base::string16();
}
bool FormatCommandLineString(base::string16* exe,