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
options.Get(options::kFullScreenable, &fullscreenable);
  SetFullScreenable(fullscreenable);
  if (fullscreen) {
    SetFullScreen(true);
  }
  bool skip;
  if (options.Get(options::kSkipTaskbar, &skip)) {
    SetSkipTaskbar(skip);
  }
  bool kiosk;
  if (options.Get(options::kKiosk, &kiosk) && kiosk) {
    SetKiosk(kiosk);
  }
  std::string color;
  if (options.Get(options::kBackgroundColor, &color)) {
    SetBackgroundColor(color);
  } else if (!transparent()) {
    
    SetBackgroundColor("#FFFF");
  }
  std::string title(Browser::Get()->GetName());
  options.Get(options::kTitle, &title);
  SetTitle(title);
  
  bool show = true;
  options.Get(options::kShow, &show);
  if (show)
    Show();
}
void NativeWindow::SetSize(const gfx::Size& size, bool animate) {