mParentFrame->FirstChild(mPresContext, nsnull, &mCurrentChild);
mCurrentChild = mParentFrame->GetFirstChild(nsnull);
nsFrameContentIterator::First(){  // Get the first child frame and make it the current node  mParentFrame->FirstChild(mPresContext, nsnull, &mCurrentChild);  if (!mCurrentChild) {    return NS_ERROR_FAILURE;  }  mIsDone = PR_FALSE;  return NS_OK;}