### 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
gfx::Size size;
  bool stay_hidden = false;
  // get size arguments if they exist
  args->GetNext(&size);
  // get stayHidden arguments if they exist
  args->GetNext(&stay_hidden);
  ontents()->IncrementCapturerCount(size, stay_hidden);
}
void Ws::DecrementCapturerCount(gin_helper::Arguments* args) {
  bool stay_hidden = false;
  // get stayHidden arguments if they exist
  args->GetNext(&stay_hidden);
  ontents()->DecrementCapturerCount(stay_hidden);
}
bool Ws::IsBeingCaptured() {
  return ontents()->IsBeingCaptured();
}
void Ws::OnCursorChange(const content::WebCursor& cursor) {
  const content::CursorInfo& info = cursor.info();
  if (info.type == ui::CursorType::kCustom) {
    Emit("cursor-changed", CursorTypeToString(info),
         gfx::Image::CreateFrom1xBitmap(info.custom_image),
         info.image_scale_factor,
         gfx::Size(info.custom_image.width(), info.custom_image.height()),
         info.hotspot);
  } else {
    Emit("cursor-changed", CursorTypeToString(info));
  }
}
bool Ws::IsGuest() const {