addXObject method
Add an XObject to this graphic object
Implementation
void addXObject(PdfXObject object) {
  if (!xObjects.containsKey(object.name)) {
    xObjects[object.name] = object;
  }
}
Add an XObject to this graphic object
void addXObject(PdfXObject object) {
  if (!xObjects.containsKey(object.name)) {
    xObjects[object.name] = object;
  }
}