### 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
sender_id);
  }
  return true;
}
bool Ws::SendIPCMessageToFrame(bool internal,
                                        bool send_to_all,
                                        int32_t frame_id,
                                        const std::string& channel,
                                        v8::Local<v8::Value> args) {
  blink::CloneableMessage message;
  if (!gin::ConvertFromV8(isolate(), args, &message)) {
    isolate()->ThrowException(v8::Exception::Error(
        gin::StringToV8(isolate(), "Failed to serialize arguments")));
    return false;
  }
  auto frames = ontents()->GetAllFrames();
  auto iter = std::find_if(frames.begin(), frames.end(), [frame_id](auto* f) {
    return f->GetRoutingID() == frame_id;
  });
  if (iter == frames.end())
    return false;
  if (!(*iter)->IsRenderFrameLive())
    return false;
  mojo::AssociatedRemote<mojom::ElectronRenderer> electron_renderer;
  (*iter)->GetRemoteAssociatedInterfaces()->GetInterface(&electron_renderer);
  electron_renderer->Message(internal, send_to_all, channel, std::move(message),
                             0 /* sender_id */);
  return true;
}
void Ws::SendInputEvent(v8::Isolate* isolate,