* Output of `node_modules/.bin/electron --version`:
v3.0.6
v4.0.0-beta.5

* Operating System (Platform and Version):
macOS High Siearra 10.13.6

* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable):
v2.0.11

**Expected Behavior**
BrowserWindow.getNativeWindowHandle() must return non-nullable result.

**Actual behavior**
BrowserWindow.getNativeWindowHandle() returns null.

**To Reproduce**

***Sample code***
```
const { app, BrowserWindow } = require('electron');

let win

app
	.on('ready', () => {
		win = new BrowserWindow({width: 800, height: 600})
		win.loadURL('https://www.google.com')
		
		win.on('closed', () => win = null);

		const handle = win.getNativeWindowHandle();
		console.log('Current window: ' + handle.toString('hex'));
	})
	.on('window-all-closed', () => app.quit());
```

***Expected output***
Something different than `Current window: 0000000000000000`

***Actual output***
`Current window: 0000000000000000`
atom/browser/api/atom_api_top_level_window.cc
base::string16 app_id;
  base::FilePath app_icon_path;
  int app_icon_index = 0;
  base::string16 relaunch_command;
  base::string16 relaunch_display_name;
  options.Get("appId", &app_id);
  options.Get("appIconPath", &app_icon_path);
  options.Get("appIconIndex", &app_icon_index);
  options.Get("relaunchCommand", &relaunch_command);
  options.Get("relaunchDisplayName", &relaunch_display_name);
  ui::win::SetAppDetailsForWindow(app_id, app_icon_path, app_icon_index,
                                  relaunch_command, relaunch_display_name,
                                  window_->GetAcceleratedWidget());
}
#endif
int32_t TopLevelWindow::GetID() const {
  return weak_map_id();
}
void TopLevelWindow::ResetBrowserView() {
  if (browser_view_.IsEmpty())
    return;
  mate::Handle<BrowserView> browser_view;
  if (mate::ConvertFromV8(isolate(), GetBrowserView(), &browser_view) &&
      !browser_view.IsEmpty()) {
    browser_view->web_contents()->SetOwnerWindow(nullptr);
  }
  browser_view_.Reset();
}
void TopLevelWindow::RemoveFromParentChildWindows() {