* 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
window_icon_ = base::win::ScopedHICON(CopyIcon(window_icon));
  app_icon_ = base::win::ScopedHICON(CopyIcon(app_icon));
  HWND hwnd = GetAcceleratedWidget();
  SendMessage(hwnd, WM_SETICON, ICON_SMALL,
              reinterpret_cast<LPARAM>(window_icon_.get()));
  SendMessage(hwnd, WM_SETICON, ICON_BIG,
              reinterpret_cast<LPARAM>(app_icon_.get()));
}
#elif defined(USE_X11)
void NativeWindowViews::SetIcon(const gfx::ImageSkia& icon) {
  auto* tree_host = static_cast<views::DesktopWindowTreeHost*>(
      views::DesktopWindowTreeHostX11::GetHostForXID(GetAcceleratedWidget()));
  tree_host->SetWindowIcons(icon, icon);
}
#endif
void NativeWindowViews::OnWidgetActivationChanged(views::Widget* changed_widget,
                                                  bool active) {
  if (changed_widget != widget())
    return;
  if (active)
    NativeWindow::NotifyWindowFocus();
  else
    NativeWindow::NotifyWindowBlur();
  
  if (!active && IsMenuBarAutoHide() && IsMenuBarVisible())
    SetMenuBarVisibility(false);
  root_view_->ResetAltState();
}
void NativeWindowViews::OnWidgetBoundsChanged(views::Widget* changed_widget,