I just tested my site in Chrome latest.
The dev tools panel does indeed show “index.php” under “sources”
- but -
what is shown as the code is what is output to the browser (i.e. HTML) not the PHP code of the file.
Admittedly, it is a bit misleading as “sources” displays as a “tree”, and it is possible to see any CSS and JavaScript so one could get the impression that seeing the PHP code is also possible, but AFAIK it is not (unless as previously mentioned the PHP engine is down)