rv = ArenaImpl::Create(NULL, nsIArena::GetIID(), (void**)&arena);
rv = ArenaImpl::Create(NULL, NS_GET_IID(nsIArena), (void**)&arena);
NS_COM nsresult NS_NewHeapArena(nsIArena** aInstancePtrResult,                                 PRUint32 aArenaBlockSize){  nsresult rv;  nsIArena* arena;  rv = ArenaImpl::Create(NULL, nsIArena::GetIID(), (void**)&arena);  if (NS_FAILED(rv)) return rv;      rv = arena->Init(aArenaBlockSize);  if (NS_FAILED(rv)) {    NS_RELEASE(arena);    return rv;  }        *aInstancePtrResult = arena;  return rv;}