if (mPresShell)
if (mPresShell && !mSharedPresShell)
PrintObject::~PrintObject(){  for (PRInt32 i=0;i<mKids.Count();i++) {    PrintObject* po = (PrintObject*)mKids[i];    NS_ASSERTION(po, "PrintObject can't be null!");    delete po;  }   if (mPresShell)    mPresShell->Destroy();}