code: function (progressListener) {
              var self = this, listeners = self[PROMISE_PROGRESS_LISTENERS];
              if (listeners === false) {
                  return self;
              }
              if (!listeners) {
                  listeners = self[PROMISE_PROGRESS_LISTENERS] = [];
              }
              listeners.push(progressListener);
              return self;
          }
docs: call progress listener when defer.notify is called
  @param {Function} [progressListener] progress listener