rxgroups/src/main/java/com/airbnb/rxgroups/ObservableGroup.java
public <T> Observable<T> observable(Observer<? super T> observer) {
    return observable(observer, Utils.getObserverTag(observer));
  }
public <T> Observable<T> observable(Observer<? super T> observer) {
    return observable(observer, Utils.getObserverTag(observer));
  }
Returns an existing {@link Observable} for the {@link TaggedObserver}.
<p>
<p> Does not change the locked status of this {@link ObservableGroup}.
If it is unlocked, and the Observable has already emitted events,
they will be immediately delivered. If it is locked then no events will be
delivered until it is unlocked.