* Output of `node_modules/.bin/electron --version`: 4.0.0-beta.8
* Operating System (Platform and Version): Windows 10 1803
* Output of `node_modules/.bin/electron --version` on last known working Electron version (if applicable): 4.0.0-beta.7

**Expected Behavior**
`BrowserWindow.getNativeWindowHandle()` should return different value for different window

**Actual behavior**
`BrowserWindow.getNativeWindowHandle()` returns same value for different window, which is not true nativeWindowHandle for any of them.

**To Reproduce**
Open two `BrowserWindow`, and run `getNativeWindowHandle` on both `BrowserWindow`
```js
const { remote } = require('electron')
w1 = new remote.BrowserWindow()
w2 = new remote.BrowserWindow()
console.log(w1.getNativeWindowHandle(), w2.getNativeWindowHandle())
```
![image](https://user-images.githubusercontent.com/8194131/49328509-7411a800-f5b5-11e8-9a24-827aa589d937.png)


atom/browser/native_window_views.cc
NotifyWindowMove();
}
void NativeWindowViews::HandleKeyboardEvent(
    content::WebContents*,
    const content::NativeWebKeyboardEvent& event) {
#if defined(OS_LINUX)
  if (event.windows_key_code == ui::VKEY_BROWSER_BACK)
    NotifyWindowExecuteAppCommand(kBrowserBackward);
  else if (event.windows_key_code == ui::VKEY_BROWSER_FORWARD)
    NotifyWindowExecuteAppCommand(kBrowserForward);
#endif
  keyboard_event_handler_->HandleKeyboardEvent(event,
                                               root_view_->GetFocusManager());
  root_view_->HandleKeyEvent(event);
}
#if defined(OS_LINUX)
void NativeWindowViews::OnMouseEvent(ui::MouseEvent* event) {