code: public final void registerForActivityResult(final int requestCode) {
          executeWithRouter(new RouterRequiringFunc() {
              @Override public void execute() { router.registerForActivityResult(instanceId, requestCode); }
          });
      }
docs: Registers this Controller to handle onActivityResult responses. Calling this method is NOT
  necessary when calling {@link #startActivityForResult(Intent, int)}
  
  @param requestCode The request code being registered for.