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.h
void UnhookAllWindowMessages();
  bool SetThumbnailClip(const gfx::Rect& region);
#endif
#if defined(TOOLKIT_VIEWS)
  void SetIcon(mate::Handle<NativeImage> icon);
#endif
  void SetVisibleOnAllWorkspaces(bool visible);
  bool IsVisibleOnAllWorkspaces();
  int32_t ID() const;
  v8::Local<v8::Value> WebContents(v8::Isolate* isolate);
  
  void RemoveFromParentChildWindows();
#if defined(OS_WIN)
  typedef std::map<UINT, MessageCallback> MessageCallbackMap;
  MessageCallbackMap messages_callback_map_;
#endif
  v8::Global<v8::Value> web_contents_;
  v8::Global<v8::Value> menu_;
  v8::Global<v8::Value> parent_window_;
  KeyWeakMap<int> child_windows_;
  api::WebContents* api_web_contents_;
  std::unique_ptr<NativeWindow> window_;
  DISALLOW_COPY_AND_ASSIGN(Window);
};
}  
}  
namespace mate {
template<>
struct Converter<atom::NativeWindow*> {
  static bool FromV8(v8::Isolate* isolate, v8::Local<v8::Value> val,