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.cc
brightray::InspectableWebContents* inspectable_web_contents,
    const mate::Dictionary& options,
    NativeWindow* parent)
    : content::WebContentsObserver(inspectable_web_contents->GetWebContents()),
      has_frame_(true),
      transparent_(false),
      enable_larger_than_screen_(false),
      is_closed_(false),
      sheet_offset_x_(0.0),
      sheet_offset_y_(0.0),
      aspect_ratio_(0.0),
      parent_(parent),
      is_modal_(false),
      inspectable_web_contents_(inspectable_web_contents),
      weak_factory_(this) {
  options.Get(options::kFrame, &has_frame_);
  options.Get(options::kTransparent, &transparent_);
  options.Get(options::kEnableLargerThanScreen, &enable_larger_than_screen_);
  if (parent)
    options.Get("modal", &is_modal_);
#if defined(OS_LINUX) || defined(OS_WIN)
  auto* prefs = web_contents()->GetMutableRendererPrefs();