### 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

* **Electron Version:**
10.0.0-nightly.20200220
* **Operating System:**
macOS 10.15.1
* **Last Known Working Electron version:**
I don't know (judging by implementation it never worked)

### Expected Behavior:
Call to BrowserWindow.webContents.focus focuses proper window

### Actual Behavior:
Call  to BrowserWindow.webContents.focus does nothing

### To Reproduce:

Run following simple app:
```
const { app, BrowserWindow } = require('electron')

function createWindow () {
  let win1 = new BrowserWindow({ x:100, y: 300, width: 300, height: 200 })
  win1.on('closed', () => {
    win1 = null
  })
  win1.loadURL('https://github.com')

  let win2 = new BrowserWindow({ x:300, y: 300, width: 300, height: 200 })
  win2.on('closed', () => {
    win1 = null
  })
  win2.loadURL('http://www.example.com')

  setTimeout(() => {
    win1.webContents.focus();
  }, 3000);
}

app.on('ready', createWindow)
```

It works as expected on Windows: it creates two windows and after three seconds it focuses the first one. On mac it doesn't work and call to `webContents.focus` doesn't change the focus (it stays on the second window).
shell/browser/api/electron_api_web_contents.cc
base::ScopedBlockingCall scoped_blocking_call(FROM_HERE,
                                                base::BlockingType::MAY_BLOCK);
  scoped_refptr<printing::PrintBackend> backend =
      printing::PrintBackend::CreateInstance(
          nullptr, g_browser_process->GetApplicationLocale());
  std::string printer_name = backend->GetDefaultPrinterName();
  return base::UTF8ToUTF16(printer_name);
}
#endif
e
Ws::Ws(v8::Isolate* isolate,
                         content::Ws* ontents)
    : content::WsObserver(ontents),
      type_(Type::REMOTE),
      weak_factory_(this) {
  ontents->SetUserAgentOverride(GetBrowserContext()->GetUserAgent(),
                                     false);
  Init(isolate);
  AttachAsUserData(ontents);
  InitZoomController(ontents, gin::Dictionary::CreateEmpty(isolate));
#if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
  extensions::ElectronExtensionWsObserver::CreateForWs(
      ontents);
  script_executor_.reset(new extensions::ScriptExecutor(ontents));
#endif
  registry_.AddInterface(base::BindRepeating(&Ws::BindElectronBrowser,
                                             base::Unretained(this)));
  bindings_.set_connection_error_handler(base::BindRepeating(
      &Ws::OnElectronBrowserConnectionError, base::Unretained(this)));