GetTracker()->GetPrimaryFrameFor(aCellContent, &cellFrame);
mShell->GetPrimaryFrameFor(aCellContent, &cellFrame);
nsSelection::GetCellLayout(nsIContent *aCellContent){  // Get frame for cell  nsIFrame *cellFrame = nsnull;  GetTracker()->GetPrimaryFrameFor(aCellContent, &cellFrame);  if (!cellFrame)    return nsnull;  nsITableCellLayout *cellLayoutObject = nsnull;  CallQueryInterface(cellFrame, &cellLayoutObject);  return cellLayoutObject;}