### 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
if (!navigation_handle->HasCommitted())
    return;
  bool is_main_frame = navigation_handle->IsInMainFrame();
  content::RenderFrameHost* frame_host =
      navigation_handle->GetRenderFrameHost();
  int frame_process_id = -1, frame_routing_id = -1;
  if (frame_host) {
    frame_process_id = frame_host->GetProcess()->GetID();
    frame_routing_id = frame_host->GetRoutingID();
  }
  if (!navigation_handle->IsErrorPage()) {
    // FIXME: All the Emit() calls below could potentially result in |this|
    // being destroyed (by JS listening for the event and calling
    // ws.destroy()).
    auto url = navigation_handle->GetURL();
    bool is_same_document = navigation_handle->IsSameDocument();
    if (is_same_document) {
      Emit("did-navigate-in-page", url, is_main_frame, frame_process_id,
           frame_routing_id);
    } else {
      const net::HttpResponseHeaders* http_response =
          navigation_handle->GetResponseHeaders();
      std::string http_status_text;
      int http_response_code = -1;
      if (http_response) {
        http_status_text = http_response->GetStatusText();
        http_response_code = http_response->response_code();
      }
      Emit("did-frame-navigate", url, http_response_code, http_status_text,
           is_main_frame, frame_process_id, frame_routing_id);