title: Androidx Activity OnBackPressedCallback Interface Issue
body: <pre><code>implementation("androidx.core:core-ktx:1.1.0-alpha04")
  implementation ("androidx.appcompat:appcompat:1.0.2")
  implementation ("androidx.activity:activity-ktx:1.0.0-alpha05")
  </code></pre>
  
  <p>I was also looking at this <a href="https://stackoverflow.com/questions/54915164/why-are-their-2-different-componentactivity-classes/54915331#54915331">Why are their 2 different ComponentActivity classes?</a>
  I have this library setup and hoping to use <strong>OnBackPressedCallback</strong></p>
  
  <pre><code>import android.os.Bundle
  import androidx.activity.OnBackPressedCallback
  import androidx.fragment.app.Fragment
  
  open class BaseNiceFragment : Fragment(), OnBackPressedCallback {
  
      override fun handleOnBackPressed(): Boolean {
         // do some nice things here
         return true
      }
  
      override fun onActivityCreated(savedInstanceState: Bundle?) {
         super.onActivityCreated(savedInstanceState)
         activity!!.addOnBackPressedCallback(viewLifecycleOwner, this)
      }
  
      override fun onDestroyView() {
         super.onDestroyView()
         activity!!.removeOnBackPressedCallback(this)
      }
  
      protected open fun handleEmptyView(isListEmpty: Boolean) {} 
  }
  </code></pre>
  
  <p>It works fine with debug builds with Android Studio but whenever I try to do a <code>app:compileFullReleaseKotlin</code>, I keep running into the following issues</p>
  
  <pre><code>BaseNiceFragment.kt: (_, _): Unresolved reference: OnBackPressedCallback
  </code></pre>
  
  <p>Anyone or Ian know how to make sure this is included in all of my builds</p>
  
  <pre><code>public interface OnBackPressedCallback {
   //...
  }
  </code></pre>