### 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
mojom::ElectronBrowserRequest request,
    content::RenderFrameHost* render_frame_host) {
  auto id = bindings_.AddBinding(this, std::move(request), render_frame_host);
  frame_to_bindings_map_[render_frame_host].push_back(id);
}
void Ws::OnElectronBrowserConnectionError() {
  auto binding_id = bindings_.dispatch_binding();
  auto* frame_host = bindings_.dispatch_context();
  base::Erase(frame_to_bindings_map_[frame_host], binding_id);
}
void Ws::Message(bool internal,
                          const std::string& channel,
                          blink::CloneableMessage arguments) {
  TRACE_EVENT1("electron", "Ws::Message", "channel", channel);
  // ws.emit('-ipc-message', new Event(), internal, channel,
  // arguments);
  EmitWithSender("-ipc-message", bindings_.dispatch_context(), InvokeCallback(),
                 internal, channel, std::move(arguments));
}
void Ws::Invoke(bool internal,
                         const std::string& channel,
                         blink::CloneableMessage arguments,
                         InvokeCallback callback) {
  TRACE_EVENT1("electron", "Ws::Invoke", "channel", channel);
  // ws.emit('-ipc-invoke', new Event(), internal, channel, arguments);
  EmitWithSender("-ipc-invoke", bindings_.dispatch_context(),
                 std::move(callback), internal, channel, std::move(arguments));
}
void Ws::MessageSync(bool internal,