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
views::Widget* widget, bool active) {
  if (widget != window_.get())
    return;
  
  content::BrowserThread::PostTask(
      content::BrowserThread::UI, FROM_HERE,
      base::Bind(active ? &NativeWindow::NotifyWindowFocus :
                          &NativeWindow::NotifyWindowBlur,
                 GetWeakPtr()));
  if (active && inspectable_web_contents() &&
      !inspectable_web_contents()->IsDevToolsViewShowing())
    web_contents()->Focus();
  
  if (!active && menu_bar_autohide_ && menu_bar_visible_)
    SetMenuBarVisibility(false);
}
void NativeWindowViews::OnWidgetBoundsChanged(
    views::Widget* widget, const gfx::Rect& bounds) {
  if (widget != window_.get())
    return;
  if (widget_size_ != bounds.size()) {
    NotifyWindowResize();
    widget_size_ = bounds.size();
  }
}
void NativeWindowViews::DeleteDelegate() {