nsIFrame* sib; for (lastChild->GetNextSibling(&sib); sib; sib->GetNextSibling(&sib)) { lastChild = sib; }
nsFrameItems::AddChild(nsIFrame* aChild){  if (childList == nsnull) {    childList = lastChild = aChild;  }  else  {    lastChild->SetNextSibling(aChild);    lastChild = aChild;  }}