mParent = aParent; return NS_OK;
nsCOMPtr<nsIDocShellTreeItem> parentAsTreeItem(do_QueryInterface(aParent));  mParent = parentAsTreeItem.get(); return NS_OK;
NS_IMETHODIMP nsWebShell::SetParent(nsIDocShellTreeItem* aParent){  // null aParent is ok   /*   Note this doesn't do an addref on purpose.  This is because the parent   is an implied lifetime.  We don't want to create a cycle by refcounting   the parent.   */   mParent = aParent;  return NS_OK;}