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 (menu_model == nullptr) {
    
    accelerator_table_.clear();
    GetFocusManager()->UnregisterAccelerators(this);
    
#if defined(USE_X11)
    global_menu_bar_.reset();
#endif
    SetMenuBarVisibility(false);
    menu_bar_.reset();
    return;
  }
  RegisterAccelerators(menu_model);
#if defined(USE_X11)
  if (!global_menu_bar_ && ShouldUseGlobalMenuBar())
    global_menu_bar_.reset(new GlobalMenuBarX11(this));
  
  if (global_menu_bar_ && global_menu_bar_->IsServerStarted()) {
    global_menu_bar_->SetMenu(menu_model);
    return;
  }
#endif
  
  if (!has_frame())