code: function(args) {
          base.call(this, args);
          this.loadedOnceDeferred = new $.Deferred();
          this.loadedOnce = false;
          this.loadingCount = 0;
          // Loading is a convenience flag that is the equivalent of loadingCount > 0
          this.loading = false;
        }
docs: Adds the loading mixin
  @method constructor
  @param args {Object} the arguments to the base constructor method