Thanks for your request. As this has received few votes over 4 years, the request has now been closed and archived.
Upstream chromium code handles the source viewer and at the moment the developers do not have the resources to work on this.
If you want, you could make a request to the chromium project for this feature.
I moved this topic to the Done category and closed it since most of it is implemented already. Feel free to create a new feature request for the remaining feature. 🙂
Thanks everyone for your input and remember to post only one feature per request. 😉