function TapObservable(source, observerOrOnNext, onError, onCompleted) {
      this.source = source;
      this._oN = observerOrOnNext;
      this._oE = onError;
      this._oC = onCompleted;
      __super__.call(this);
    }
Returns an observable sequence that contains only distinct contiguous elements according to the keyFn and the comparer.
@param {Function} [keyFn] A function to compute the comparison key for each element. If not provided, it projects the value.
@param {Function} [comparer] Equality comparer for computed key values. If not provided, defaults to an equality comparer function.
@returns {Observable} An observable sequence only containing the distinct contiguous elements, based on a computed key value, from the source sequence.