### 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
}
Ws::Ws(v8::Isolate* isolate,
                         std::unique_ptr<content::Ws> ontents,
                         Type type)
    : content::WsObserver(ontents.get()),
      type_(type),
      weak_factory_(this) {
  DCHECK(type != Type::REMOTE)
      << "Can't take ownership of a remote Ws";
  auto session = Session::CreateFrom(isolate, GetBrowserContext());
  session_.Reset(isolate, session.ToV8());
  InitWithSessionAndOptions(isolate, std::move(ontents), session,
                            gin::Dictionary::CreateEmpty(isolate));
}
Ws::Ws(v8::Isolate* isolate,
                         const gin_helper::Dictionary& options)
    : weak_factory_(this) {
  
  options.Get("backgroundThrottling", &background_throttling_);
  
  options.Get("type", &type_);
#if BUILDFLAG(ENABLE_OSR)
  bool b = false;
  if (options.Get(options::kOffscreen, &b) && b)
    type_ = Type::OFF_SCREEN;
#endif
  
  options.Get("embedder", &embedder_);
  
  options.Get("devTools", &enable_devtools_);