NS_ASSERTION(mLast, "No last node!");
mIsDone = mLast == nsnull;
nsContentIterator::Last(){  NS_ASSERTION(mLast, "No last node!");  if (mLast) {#ifdef DEBUG    nsresult rv =#endif    PositionAt(mLast);    NS_ASSERTION(NS_SUCCEEDED(rv), "Failed to position iterator!");  }  mIsDone = mLast == nsnull;}