code: public Observable<UsageListResultInner> listAsync(String location) {
          return listWithServiceResponseAsync(location).map(new Func1<ServiceResponse<UsageListResultInner>, UsageListResultInner>() {
              @Override
              public UsageListResultInner call(ServiceResponse<UsageListResultInner> response) {
                  return response.body();
              }
          });
      }
docs: Get the usage for a subscription.
  
  @param location The identifier for the physical azure location.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the UsageListResultInner object