NS_ASSERTION(parent, "undisplayed content must have a parent");
FrameManager::SetUndisplayedContent(nsIContent* aContent,                                     nsIStyleContext* aStyleContext){  NS_ENSURE_TRUE(mPresShell, NS_ERROR_NOT_AVAILABLE);  if (! mUndisplayedMap) {    mUndisplayedMap = new UndisplayedMap;  }  if (mUndisplayedMap) {    nsresult result = NS_OK;    nsIContent* parent = nsnull;    aContent->GetParent(parent);    if (parent) {      result = mUndisplayedMap->AddNodeFor(parent, aContent, aStyleContext);      NS_RELEASE(parent);    }    return result;  }  return NS_ERROR_OUT_OF_MEMORY;}