* 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
SetFullScreen(simple_fullscreen);
}
bool NativeWindowViews::IsSimpleFullScreen() {
  return IsFullscreen();
}
void NativeWindowViews::SetKiosk(bool kiosk) {
  SetFullScreen(kiosk);
}
bool NativeWindowViews::IsKiosk() {
  return IsFullscreen();
}
void NativeWindowViews::SetBackgroundColor(SkColor background_color) {
  
  root_view_->SetBackground(views::CreateSolidBackground(background_color));
#if defined(OS_WIN)
  
  HBRUSH brush = CreateSolidBrush(skia::SkColorToCOLORREF(background_color));
  ULONG_PTR previous_brush =
      SetClassLongPtr(GetAcceleratedWidget(), GCLP_HBRBACKGROUND,
                      reinterpret_cast<LONG_PTR>(brush));
  if (previous_brush)
    DeleteObject((HBRUSH)previous_brush);
  InvalidateRect(GetAcceleratedWidget(), NULL, 1);
#endif
}
void NativeWindowViews::SetHasShadow(bool has_shadow) {