code: function(layer) {
              var layers = this.layers,
                  len, n;
  
              if (layers) {
                  len = layers.length;
  
                  // don't add the layer if it already exists
                  for (n = 0; n < len; n++) {
                      if (layers[n]._id === layer._id) {
                          return false;
                      }
                  }
              }
              else {
                  this.layers = [];
              }
  
              this.layers.push(layer);
              return true;
          }
docs: add layer.  Returns true if the layer was added, and false if it was not
  @method
  @memberof Kinetic.Animation.prototype
  @param {Kinetic.Layer} layer