code: function ScrollAction(opt_callback, opt_distance_func) {
      var self = this;
  
      this.beginMeasuringHook = function() {}
      this.endMeasuringHook = function() {}
  
      this.callback_ = opt_callback;
      this.distance_func_ = opt_distance_func;
    }
docs: This class scrolls a page from the top to the bottom once.  The page is scrolled down by a single scroll gesture.