* 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 defined(OS_WIN)
  return minimizable_;
#elif defined(USE_X11)
  return true;
#endif
}
base::string16 NativeWindowViews::GetWindowTitle() const {
  return base::UTF8ToUTF16(title_);
}
views::View* NativeWindowViews::GetContentsView() {
  return root_view_.get();
}
bool NativeWindowViews::ShouldDescendIntoChildForEventHandling(
    gfx::NativeView child,
    const gfx::Point& location) {
  
  if (draggable_region() &&
      draggable_region()->contains(location.x(), location.y()))
    return false;
  
  if (!has_frame() && CanResize()) {
    FramelessView* frame =
        static_cast<FramelessView*>(widget()->non_client_view()->frame_view());
    return frame->ResizingBorderHitTest(location) == HTNOWHERE;
  }
  return true;
}
views::ClientView* NativeWindowViews::CreateClientView(views::Widget* widget) {