I did it before, but the title bar was not shown when I returned to the windowed mode.
I think the window property seems to be changed by other method:
```
void NativeWidgetAura::SetFullscreen(bool fullscreen) {
  if (!window_ || IsFullscreen() == fullscreen)
    return;  // Nothing to do.

  // Save window state before entering full screen so that it could restored
  // when exiting full screen.
  if (fullscreen)
    saved_window_state_ = window_->GetProperty(aura::client::kShowStateKey);

  window_->SetProperty(
      aura::client::kShowStateKey,
      fullscreen ? ui::SHOW_STATE_FULLSCREEN : saved_window_state_);
} 
```