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
SetBounds(gfx::Rect(GetPosition(), size), animate);
}
gfx::Size NativeWindow::GetSize() {
  return GetBounds().size();
}
void NativeWindow::SetPosition(const gfx::Point& position, bool animate) {
  SetBounds(gfx::Rect(position, GetSize()), animate);
}
gfx::Point NativeWindow::GetPosition() {
  return GetBounds().origin();
}
void NativeWindow::SetContentSize(const gfx::Size& size, bool animate) {
  SetSize(ContentSizeToWindowSize(size), animate);
}
gfx::Size NativeWindow::GetContentSize() {
  return WindowSizeToContentSize(GetSize());
}
void NativeWindow::SetSizeConstraints(
    const extensions::SizeConstraints& window_constraints) {
  extensions::SizeConstraints content_constraints(GetContentSizeConstraints());
  if (window_constraints.HasMaximumSize())
    content_constraints.set_maximum_size(
        WindowSizeToContentSize(window_constraints.GetMaximumSize()));
  if (window_constraints.HasMinimumSize())
    content_constraints.set_minimum_size(
        WindowSizeToContentSize(window_constraints.GetMinimumSize()));
  SetContentSizeConstraints(content_constraints);
}
extensions::SizeConstraints NativeWindow::GetSizeConstraints() {