title: Flutter drag down to pop ModalRoute page
body: <p>Hei i have app like this</p>
  
  <p><a href="https://i.stack.imgur.com/PbpfR.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PbpfR.gif" alt="enter image description here"></a></p>
  
  <p>my question is how can this modal route draggable down to pop route?
  this popup page i create from this sample <a href="https://stackoverflow.com/a/51908876/10068765">https://stackoverflow.com/a/51908876/10068765</a></p>
  
  <p>i tried with backdrop on flutter example but its not work, can anyone help with a sample gesturedetector to pop this modal route ?
  thanks.</p>