title: Android onBackPressed handling with new Navigation component
body: <p>I need some suggestions;</p>
  
  <p>I'm experimenting with Navigation library. I have a fragment which has a webView. I want to check if it <code>canGoBack</code> and do so if it can, otherwise not interfere.</p>
  
  <p><strong>1. Interface approach</strong>: Since Navigation is handling transactions, I don't create an instance of my fragment manually anymore, which I can assign as a listener in activity.</p>
  
  <p><strong>1. Key listening:</strong> I really think it looks ugly and I don't think it's a generic solution, so I skip this one.</p>
  
  <p>I need some opinions on how can it be done with Navigation library. When you try to get <code>currentDestination</code> from <code>navController</code>, it's <code>NavigationDestination</code> object which provides information about current fragment, such as label given in xml. </p>
  
  <p>When I inspect <code>fragmentManager</code>, I see that <code>backStack</code> is empty &amp; fragment transaction took place without a tag. </p>
  
  <p>IMHO it wouldn't fit the concept of the library to do <code>findFragment</code> kind of operations to somewhat interact with current fragment, but I can't seem to find a way through with it at the moment. Any suggestions ?</p>