title: addToBackstack not working when replacing fragments
body: <p>I am having an issue where I call <code>addToBackStack</code> on my fragment when replacing it, but when I press back to go back to that fragment, it doesn't go back, it just closes my app.</p>
  
  <pre><code>Fragment fragmentWebView = new MyWebView();
  transaction.replace(R.id.content_frame, fragmentWebView);
  transaction.addToBackStack(null);
  transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
  transaction.commit();
  </code></pre>
  
  <p>Am I doing anything wrong here? everything looks fine to me.</p>