code: function giveStore(ecModel) {
      var store = ecModel[ATTR];
      if (!store) {
          store = ecModel[ATTR] = [{}];
      }
      return store;
  }
docs: [{key: dataZoomId, value: {dataZoomId, range}}, ...]
  History length of each dataZoom may be different.
  this._history[0] is used to store origin range.
  @type {Array.<Object>}