code: public static LinkedBindingBuilder<HttpClientObserver> bindNewObserver(final Binder binder, final HttpClientObserverGroup observerGroup)
      {
          return MapBinder.newMapBinder(binder, HttpClientObserverGroup.class, HttpClientObserver.class, Names.named(OBSERVER_GROUP)).permitDuplicates().addBinding(observerGroup);
      }
docs: Register a HttpClientObserver which observes requests from any HttpClient that is given the specified
  {@link HttpClientObserverGroup}.