title: How to use Android Fragment in Flutter plugin?
body: <p>I need to wrap SDK created in native code iOS/Android into Flutter. On Android side there is some functionality where my Fragment or Activity needs to extend <strong>SDK</strong> Fragment or Activity to implement custom view.
  My question is how I can wrap <strong>SDK</strong> Fragment or Activity in <strong>Flutter plugin</strong> and let extends this on flutter project side using my plugin ? I other words I would like to have a Widget which can extend Fragment or Activity using my plugin to have <strong>ability to show Widget ui in SDK</strong>.</p>
  <p>Using FlutterFragment, FlutterActivity in plugin is right way ?</p>
  <p>I mean:
  Flutter project (Widget) &lt;-&gt; Flutter plugin (FlutterFragment or FlutterActivity attached to native SDK Fragment or Activity)</p>
  <p>If not what is a possible solution ?</p>