function LastObservable(source, obj) {
      this.source = source;
      this._obj = obj;
      __super__.call(this);
    }
Returns the first element of an observable sequence that satisfies the condition in the predicate if present else the first item in the sequence.
@returns {Observable} Sequence containing the first element in the observable sequence that satisfies the condition in the predicate if provided, else the first item in the sequence.