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
extensions::SizeConstraints content_constraints = GetContentSizeConstraints();
  extensions::SizeConstraints window_constraints;
  if (content_constraints.HasMaximumSize())
    window_constraints.set_maximum_size(
        ContentSizeToWindowSize(content_constraints.GetMaximumSize()));
  if (content_constraints.HasMinimumSize())
    window_constraints.set_minimum_size(
        ContentSizeToWindowSize(content_constraints.GetMinimumSize()));
  return window_constraints;
}
void NativeWindow::SetContentSizeConstraints(
    const extensions::SizeConstraints& size_constraints) {
  size_constraints_ = size_constraints;
}
extensions::SizeConstraints NativeWindow::GetContentSizeConstraints() {
  return size_constraints_;
}
void NativeWindow::SetMinimumSize(const gfx::Size& size) {
  extensions::SizeConstraints size_constraints;
  size_constraints.set_minimum_size(size);
  SetSizeConstraints(size_constraints);
}
gfx::Size NativeWindow::GetMinimumSize() {
  return GetSizeConstraints().GetMinimumSize();
}
void NativeWindow::SetMaximumSize(const gfx::Size& size) {