code: function _getRequiredAdCountForAdUnit(adUnit) {
      var adContainers = page.getAdContainers(adUnit);
  
      if (!adContainers.length) {
          return 0;
      }
  
      var numberOfAdsToInsert = 0;
      for (var i = 0; i < adContainers.length; i++) {
          var adContainer = adContainers[i];
          numberOfAdsToInsert += adContainer.getNumberOfAdsToInsert();
      }
  
      return numberOfAdsToInsert;
  }
docs: Get the number of ads this unit needs to place all the ads on the page
  @param adUnit The ad unit to get the required number of ads for
  @returns {number} the number of required ads
  @private