title: perform scroll using AccessibilityNodeInfo in AccessibilityService
body: <p>i want to Scroll the current screen.
  i tried this <code>
  AccessibilityNodeInfo accessibilityNodeInfo=getRootInActiveWindow();
  accessibilityNodeInfo.addAction(AccessibilityNodeInfo.AccessibilityAction.ACTION_SCROLL_DOWN);
  </code>
  but i always say "Cannot perform this action on a sealed instance".
  help please.</p>