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/api/atom_api_window.cc
gfx::Size extra_size;
  args->GetNext(&extra_size);
  window_->SetAspectRatio(aspect_ratio, extra_size);
}
void Window::SetParentWindow(v8::Local<v8::Value> value,
                             mate::Arguments* args) {
  if (IsModal()) {
    args->ThrowError("Can not be called for modal window");
    return;
  }
  mate::Handle<Window> parent;
  if (value->IsNull()) {
    RemoveFromParentChildWindows();
    parent_window_.Reset();
    window_->SetParentWindow(nullptr);
  } else if (mate::ConvertFromV8(isolate(), value, &parent)) {
    parent_window_.Reset(isolate(), value);
    window_->SetParentWindow(parent->window_.get());
    parent->child_windows_.Set(isolate(), ID(), GetWrapper());
  } else {
    args->ThrowError("Must pass BrowserWindow instance or null");
  }
}
v8::Local<v8::Value> Window::GetParentWindow() const {