We can get the content size and the window size, but not the chrome position.

At the moment we do this:

```
leftBorderWidth = (windowWidth - contentWidth) / 2;
titlebarHeight = windowHeight - (contentHeight + leftBorderWidth);
```

which makes some assumptions so therefore feels a bit wrong.

it would be nice if alongside getContentSize (https://github.com/electron/electron/blob/master/docs/api/browser-window.md#wingetcontentsize) there was a getContentOffset.

I've been looking at the C++ - https://github.com/electron/electron/blob/e05804848f98959d63337aacd9047cd579c5b23f/chromium_src/extensions/browser/app_window/size_constraints.cc and I don't see an easy way to get this information - do you have any ideas or pointers if you accept this as a feature request?

atom/browser/native_window_views.cc
if (is_modal() && NativeWindow::parent())
    static_cast<NativeWindowViews*>(NativeWindow::parent())->SetEnabled(false);
  window_->native_widget_private()->ShowWithWindowState(GetRestoredState());
  NotifyWindowShow();
#if defined(USE_X11)
  if (global_menu_bar_)
    global_menu_bar_->OnWindowMapped();
#endif
}
void NativeWindowViews::ShowInactive() {
  window_->ShowInactive();
  NotifyWindowShow();
#if defined(USE_X11)
  if (global_menu_bar_)
    global_menu_bar_->OnWindowMapped();
#endif
}
void NativeWindowViews::Hide() {
  if (is_modal() && NativeWindow::parent())
    static_cast<NativeWindowViews*>(NativeWindow::parent())->SetEnabled(true);
  window_->Hide();
  NotifyWindowHide();
#if defined(USE_X11)
  if (global_menu_bar_)
    global_menu_bar_->OnWindowUnmapped();
#endif
}
bool NativeWindowViews::IsVisible() {