aResult = viewer;
*aResult = viewer;
DocumentViewerImpl::CreateDocumentViewerUsing(nsIPresContext* aPresContext,                                              nsIDocumentViewer*& aResult){  if (!mDocument) {    // XXX better error    return NS_ERROR_NULL_POINTER;  }  if (!aPresContext) {    return NS_ERROR_NULL_POINTER;  }  // Create new viewer  DocumentViewerImpl* viewer = new DocumentViewerImpl(aPresContext);  if (!viewer) {    return NS_ERROR_OUT_OF_MEMORY;  }  NS_ADDREF(viewer);  // XXX make sure the ua style sheet is used (for now; need to be  // able to specify an alternate)  viewer->SetUAStyleSheet(mUAStyleSheet);  // Bind the new viewer to the old document  nsresult rv = viewer->LoadStart(mDocument);  aResult = viewer;  return rv;}