Note: In current master (based on M111), document PiP partially works when
run with the `--enable-features=DocumentPictureInPictureAPI` command-line
flag. However, the document PiP implementation at this Chromium version is
missing fixes that have already been cherry-picked to the 5563 release
branch. Those fixes will only be available in master after the next Chromium
update (to M112).