mLastLookup = nsnull;
UndisplayedMap::RemoveNodesFor(nsIContent* aParentContent){  PLHashEntry** entry = GetEntryFor(aParentContent);  NS_ASSERTION(entry, "content not in map");  if (*entry) {    UndisplayedNode*  node = (UndisplayedNode*)((*entry)->value);    delete node;    if (entry == mLastLookup) {      mLastLookup = nsnull;    }    PL_HashTableRawRemove(mTable, entry, *entry);  }  return NS_OK;}