Set the extra_info inside YoutubeDL.process_ie_result and set only if the keys are missing
Add the 'webpage_url' field to info_dict

The url for the video page, it must allow to reproduce the result.
It's automatically set by YoutubeDL if it's missing.
Set the 'extractor_key' field in the info_dict

It's the string returned by the class method 'ie_key', which allows to retrieve the extractor with 'get_info_extractor'