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;
  if (!menu_bar_) {
    gfx::Size content_size = GetContentSize();
    menu_bar_.reset(new MenuBar);
    menu_bar_->set_owned_by_client();
    if (!menu_bar_autohide_) {
      SetMenuBarVisibility(true);
      if (use_content_size_) {
        
        extensions::SizeConstraints constraints = GetContentSizeConstraints();
        if (constraints.HasMinimumSize()) {
          gfx::Size min_size = constraints.GetMinimumSize();
          min_size.set_height(min_size.height() + kMenuBarHeight);
          constraints.set_minimum_size(min_size);
        }
        if (constraints.HasMaximumSize()) {
          gfx::Size max_size = constraints.GetMaximumSize();
          max_size.set_height(max_size.height() + kMenuBarHeight);
          constraints.set_maximum_size(max_size);
        }
        SetContentSizeConstraints(constraints);
        
        SetContentSize(content_size);
      }
    }
  }
  menu_bar_->SetMenu(menu_model);
  Layout();
}
void NativeWindowViews::SetParentWindow(NativeWindow* parent) {