code: public Observable<List<VirtualMachineSizeInner>> listAvailableSizesAsync(String resourceGroupName, String availabilitySetName) {
          return listAvailableSizesWithServiceResponseAsync(resourceGroupName, availabilitySetName).map(new Func1<ServiceResponse<List<VirtualMachineSizeInner>>, List<VirtualMachineSizeInner>>() {
              @Override
              public List<VirtualMachineSizeInner> call(ServiceResponse<List<VirtualMachineSizeInner>> response) {
                  return response.body();
              }
          });
      }
docs: Lists all available virtual machine sizes that can be used to create a new virtual machine in an existing availability set.
  
  @param resourceGroupName The name of the resource group.
  @param availabilitySetName The name of the availability set.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the List&lt;VirtualMachineSizeInner&gt; object