if (oldTextZoom == aTextZoom) return NS_OK;
NS_IMETHODIMP DocumentViewerImpl::SetTextZoom(float aTextZoom){  if (mDeviceContext) {    mDeviceContext->SetTextZoom(aTextZoom);    if (mPresContext) {      mPresContext->ClearStyleDataAndReflow();    }  }  // now set the text zoom on all children of mContainer  struct TextZoomInfo textZoomInfo = { aTextZoom };  return CallChildren(SetChildTextZoom, &textZoomInfo);}