### 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
if (scheme.empty())
    return false;
  base::win::RegKey cmd_key(HKEY_CLASSES_ROOT, scheme.c_str(), KEY_QUERY_VALUE);
  return cmd_key.Valid() && cmd_key.HasValue(L"URL Protocol");
}
base::string16 GetAppForProtocolUsingAssocQuery(const GURL& url) {
  const base::string16 url_scheme = base::ASCIIToUTF16(url.scheme());
  if (!IsValidCustomProtocol(url_scheme))
    return base::string16();
  
  
  
  
  wchar_t out_buffer[1024];
  DWORD buffer_size = base::size(out_buffer);
  HRESULT hr =
      AssocQueryString(ASSOCF_IS_PROTOCOL, ASSOCSTR_FRIENDLYAPPNAME,
                       url_scheme.c_str(), NULL, out_buffer, &buffer_size);
  if (FAILED(hr)) {
    DLOG(WARNING) << "AssocQueryString failed!";
    return base::string16();
  }
  return base::string16(out_buffer);
}
base::string16 GetAppForProtocolUsingRegistry(const GURL& url) {