nsresult  rv;  NS_PRECONDITION(nsLayoutAtoms::fixedList == aListName, "unexpected child list"); if (aListName != nsLayoutAtoms::fixedList) {
nsresult rv = NS_OK;  if (mFixedContainer.GetChildListName() == aListName) { rv = mFixedContainer.AppendFrames(this, aPresContext, aPresShell, aListName, aFrameList); } else {
ViewportFrame::AppendFrames(nsIPresContext* aPresContext,                            nsIPresShell&   aPresShell,                            nsIAtom*        aListName,                            nsIFrame*       aFrameList){  nsresult  rv;    NS_PRECONDITION(nsLayoutAtoms::fixedList == aListName, "unexpected child list");  if (aListName != nsLayoutAtoms::fixedList) {    // We only expect incremental changes for our fixed frames    rv = NS_ERROR_INVALID_ARG;  } else {    // Add the frames to our list of fixed position frames  #ifdef NS_DEBUG    nsFrame::VerifyDirtyBitSet(aFrameList);  #endif    mFixedFrames.AppendFrames(nsnull, aFrameList);        // Generate a reflow command to reflow the dirty frames    nsIReflowCommand* reflowCmd;    rv = NS_NewHTMLReflowCommand(&reflowCmd, this, nsIReflowCommand::ReflowDirty);    if (NS_SUCCEEDED(rv)) {      reflowCmd->SetChildListName(nsLayoutAtoms::fixedList);      aPresShell.AppendReflowCommand(reflowCmd);      NS_RELEASE(reflowCmd);    }  }  return rv;}