code: public Observable<Page<UsageInner>> listAsync() {
          return listWithServiceResponseAsync().map(new Func1<ServiceResponse<List<UsageInner>>, Page<UsageInner>>() {
              @Override
              public Page<UsageInner> call(ServiceResponse<List<UsageInner>> response) {
                  PageImpl<UsageInner> page = new PageImpl<>();
                  page.setItems(response.body());
                  return page;
              }
          });
      }
docs: Gets the current usage count and the limit for the resources under the subscription.
  
  @return the observable to the List&lt;UsageInner&gt; object