public static <T extends View> T findViewById(Activity act, int viewId) {
    // NULLSAFE_FIXME[Nullable Dereference]
    View containerView = act.getWindow().getDecorView();
    return findViewById(containerView, viewId);
  }
This method returns the reference of the View with the given Id in the layout of the Activity
passed as parameter

@param act The Activity that is using the layout with the given View
@param viewId The id of the View we want to get a reference
@return The View with the given id and type
samples/scrollperf/src/main/java/com/facebook/samples/scrollperf/util/UI.java