void MutatorAllocRegion::retire_region(HeapRegion* alloc_region,
                                       size_t allocated_bytes) {

  {- -------------------------------------------
  (1) G1CollectedHeap::retire_mutator_alloc_region() を呼び出すだけ.
      ---------------------------------------- -}

      _g1h->retire_mutator_alloc_region(alloc_region, allocated_bytes);
    }