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.cc
if (parent_window_.IsEmpty())
    return v8::Null(isolate());
  else
    return v8::Local<v8::Value>::New(isolate(), parent_window_);
}
std::vector<v8::Local<v8::Object>> Window::GetChildWindows() const {
  return child_windows_.Values(isolate());
}
bool Window::IsModal() const {
  return window_->is_modal();
}
v8::Local<v8::Value> Window::GetNativeWindowHandle() {
  gfx::AcceleratedWidget handle = window_->GetAcceleratedWidget();
  return ToBuffer(
      isolate(), static_cast<void*>(&handle), sizeof(gfx::AcceleratedWidget));
}
void Window::SetVisibleOnAllWorkspaces(bool visible) {
  return window_->SetVisibleOnAllWorkspaces(visible);
}
bool Window::IsVisibleOnAllWorkspaces() {
  return window_->IsVisibleOnAllWorkspaces();
}
int32_t Window::ID() const {