android crosswalk goback

MainActivity.java

@Override
public boolean dispatchKeyEvent(KeyEvent event) {
  if(event.getKeyCode() == KeyEvent.KEYCODE_BACK && event.getAction() != KeyEvent.ACTION_UP) { //按下有用，key up 無用
    if (mXWalkView != null && mXWalkView.getNavigationHistory().canGoBack()) {
      mXWalkView.getNavigationHistory().navigate(XWalkNavigationHistory.Direction.BACKWARD,     1);
      return true;
    }
  }

  return false;
}