Allows handling printing initiated by Browser.print()
print settings, provide custom print settings or cancel printing.
This method is invoked when engine wants to get custom print settings and decide whether it
should continue printing or not. If this method throws an exception, then printing will be
canceled. This method will not block web browser engine. It's invoked asynchronously. You can
display in this method Modal UI Print Dialog to ask user for custom print settings.
printJob - active print job. Use it to access default print settings and modify them.