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
return new NativeWindowClientView(widget, this);
}
views::NonClientFrameView* NativeWindowViews::CreateNonClientFrameView(
    views::Widget* widget) {
#if defined(OS_WIN)
  WinFrameView* frame_view = new WinFrameView;
  frame_view->Init(this, widget);
  return frame_view;
#else
  if (has_frame()) {
    return new NativeFrameView(this, widget);
  } else {
    FramelessView* frame_view = new FramelessView;
    frame_view->Init(this, widget);
    return frame_view;
  }
#endif
}
void NativeWindowViews::OnWidgetMove() {