message: Checked haven't navigated back beyond
  When pressing android back very fast, can come in onNewIntent when crumb no longer in sceneItems. Second back happens and comes in onNewIntent for first back
diff: @@ -52,11 +52,13 @@ public class SceneActivity extends ReactActivity implements DefaultHardwareBackB
  int crumb = intent.getIntExtra(CRUMB, 0);
  if (rootView.getChildCount() > 0)
  rootView.removeViewAt(0);
  + if (crumb < NavigationStackView.sceneItems.size()) {
  View view = NavigationStackView.sceneItems.get(crumb).view;
  if (view.getParent() != null)
  ((ViewGroup) view.getParent()).removeView(view);
  rootView.addView(view);
  }
  + }
  static class SceneRootViewGroup extends ReactViewGroup implements RootView {
  private boolean hasAdjustedSize = false;
  