title: Flutter app restoration; how to save the app state when the activity is killed by the system?
body: <p>I'm an android developer and I want to switch to flutter. I love the hot reload feature that allows for faster development time. The only thing that prevents me from switching so far is that flutter lacks the option to save the app state when the activity is killed. In native android the option is provided for free (<code>onSaveInstanceState(Bundle savedInstanceState)</code>). So my question is,  how can I implement the same feature in Flutter?</p>