void G1CollectedHeap::set_region_short_lived_locked(HeapRegion* hr) {

  {- -------------------------------------------
  (1) (assert)
      ---------------------------------------- -}

      assert(heap_lock_held_for_gc(),
                  "the heap lock should already be held by or for this thread");

  {- -------------------------------------------
  (1) 引数で指定された HeapRegion を _young_list に追加する.
      ---------------------------------------- -}

      _young_list->push_region(hr);

  {- -------------------------------------------
  (1) #TODO
      ---------------------------------------- -}

      g1_policy()->set_region_short_lived(hr);
    }