* 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
if (enable != is_enabled_) {
    is_enabled_ = enable;
    SetEnabledInternal(ShouldBeEnabled());
  }
}
bool NativeWindowViews::ShouldBeEnabled() {
  return is_enabled_ && (num_modal_children_ == 0);
}
void NativeWindowViews::SetEnabledInternal(bool enable) {
  if (enable && IsEnabled()) {
    return;
  } else if (!enable && !IsEnabled()) {
    return;
  }
#if defined(OS_WIN)
  ::EnableWindow(GetAcceleratedWidget(), enable);
#elif defined(USE_X11)
  views::DesktopWindowTreeHostX11* tree_host =
      views::DesktopWindowTreeHostX11::GetHostForXID(GetAcceleratedWidget());
  if (enable) {
    tree_host->RemoveEventRewriter(event_disabler_.get());
    event_disabler_.reset();
  } else {
    event_disabler_.reset(new EventDisabler);
    tree_host->AddEventRewriter(event_disabler_.get());
  }
#endif
}
void NativeWindowViews::Maximize() {