code: function (aButtons) {
  			var iButtonsEnabled = 0;
  			for (var i = 0; i < aButtons.length; i++) {
  				if (aButtons[i].getEnabled()) {
  					iButtonsEnabled++;
  					if (!this._iFirstVisibleButtonIndex) {
  						this._iFirstVisibleButtonIndex = i;
  					}
  				}
  			}
  
  			return iButtonsEnabled;
  		}
docs: Returns the number of enabled button
  Sets firstVisibleButtonIndex
  @param {array} aButtons some buttons
  @return {int} number of enabled buttons