### 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 (is_main_frame) {
        Emit("did-navigate", url, http_response_code, http_status_text);
      }
    }
    if (IsGuest())
      Emit("load-commit", url, is_main_frame);
  } else {
    auto url = navigation_handle->GetURL();
    int code = navigation_handle->GetNetErrorCode();
    auto description = net::ErrorToShortString(code);
    Emit("did-fail-provisional-load", code, description, url, is_main_frame,
         frame_process_id, frame_routing_id);
    // Do not emit "did-fail-load" for canceled requests.
    if (code != net::ERR_ABORTED)
      Emit("did-fail-load", code, description, url, is_main_frame,
           frame_process_id, frame_routing_id);
  }
}
void Ws::TitleWasSet(content::NavigationEntry* entry) {
  base::string16 final_title;
  bool explicit_set = true;
  if (entry) {
    auto title = entry->GetTitle();
    auto url = entry->GetURL();
    if (url.SchemeIsFile() && title.empty()) {
      final_title = base::UTF8ToUTF16(url.ExtractFileName());
      explicit_set = false;
    } else {
      final_title = title;
    }