protected override sealed void DestroyWindowCore(HandleRef hwnd)
{
HWND hwndChild = new HWND(hwnd.Handle);
Debug.Assert(hwndChild == _hwndChild); // Equivalency, not reference equality.
DestroyWindowOverride(_hwndChild);
// Release our reference to the child HWND. Note that we do not
// explicitly dispose this handle, because we let
// DestroyWindowOverride decide what to do with it.
_hwndChild = null;
}