This class scrolls a page from the top to the bottom once.  The page is scrolled down by a single scroll gesture.
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;
  }