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_views.cc
#if defined(OS_WIN)
  if (thick_frame_) {
    return ::GetWindowLong(GetAcceleratedWidget(), GWL_STYLE) & WS_THICKFRAME;
  } else {
    return CanResize();
  }
#else
  return CanResize();
#endif
}
void NativeWindowViews::SetMovable(bool movable) {
  movable_ = movable;
}
bool NativeWindowViews::IsMovable() {
#if defined(OS_WIN)
  return movable_;
#else
  return true;  
#endif
}
void NativeWindowViews::SetMinimizable(bool minimizable) {
#if defined(OS_WIN)
  FlipWindowStyle(GetAcceleratedWidget(), minimizable, WS_MINIMIZEBOX);
#endif
  minimizable_ = minimizable;
}
bool NativeWindowViews::IsMinimizable() {