### 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
electron::ElectronBrowserClient::SuppressRendererProcessRestartForOnce();
  }
  ontents()->GetController().GoToOffset(offset);
}
const std::string Ws::GetWebRTCIPHandlingPolicy() const {
  return ontents()->GetMutableRendererPrefs()->webrtc_ip_handling_policy;
}
void Ws::SetWebRTCIPHandlingPolicy(
    const std::string& webrtc_ip_handling_policy) {
  if (GetWebRTCIPHandlingPolicy() == webrtc_ip_handling_policy)
    return;
  ontents()->GetMutableRendererPrefs()->webrtc_ip_handling_policy =
      webrtc_ip_handling_policy;
  ontents()->SyncRendererPrefs();
}
bool Ws::IsCrashed() const {
  return ontents()->IsCrashed();
}
void Ws::SetUserAgent(const std::string& user_agent,
                               gin_helper::Arguments* args) {
  ontents()->SetUserAgentOverride(user_agent, false);
}
std::string Ws::GetUserAgent() {
  return ontents()->GetUserAgentOverride();
}
v8::Local<v8::Promise> Ws::SavePage(
    const base::FilePath& full_file_path,
    const content::SavePageType& save_type) {
  gin_helper::Promise<void> promise(isolate());
  v8::Local<v8::Promise> handle = promise.GetHandle();