code: function () {
  	    if (hasEventPageXY === undefined) {
  	      hasEventPageXY = document.createEvent && 'pageX' in document.createEvent('MouseEvent');
  	    }
  	    if (!hasEventPageXY && !isMonitoringScrollValue) {
  	      var refresh = ViewportMetrics.refreshScrollValues;
  	      ReactBrowserEventEmitter.ReactEventListener.monitorScrollValue(refresh);
  	      isMonitoringScrollValue = true;
  	    }
  	  }
docs: Listens to window scroll and resize events. We cache scroll values so that
  application code can access them without triggering reflows.
  
  ViewportMetrics is only used by SyntheticMouse/TouchEvent and only when
  pageX/pageY isn't supported (legacy browsers).
  
  NOTE: Scroll events do not bubble.
  
  @see http://www.quirksmode.org/dom/events/scroll.html