* 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/native_window_views.cc
NativeWindow* parent)
    : NativeWindow(options, parent),
      root_view_(new RootView(this)),
      keyboard_event_handler_(new views::UnhandledKeyboardEventHandler) {
  options.Get(options::kTitle, &title_);
  bool menu_bar_autohide;
  if (options.Get(options::kAutoHideMenuBar, &menu_bar_autohide))
    root_view_->SetAutoHideMenuBar(menu_bar_autohide);
#if defined(OS_WIN)
  
  
  options.Get(options::kResizable, &resizable_);
  options.Get(options::kMinimizable, &minimizable_);
  options.Get(options::kMaximizable, &maximizable_);
  
  options.Get("thickFrame", &thick_frame_);
  if (transparent())
    thick_frame_ = false;
#endif
  if (enable_larger_than_screen())
    
    
    
    
    SetContentSizeConstraints(extensions::SizeConstraints(
        gfx::Size(), gfx::Size(INT_MAX / 10, INT_MAX / 10)));
  int width = 800, height = 600;
  options.Get(options::kWidth, &width);