If you were running chrome as a non-root user there was no way it could
have modified the file /etc/apt/sources/list. Even if you were running
it as root I'm not sure how it would have occasion to access that
particular file.

Just off the top of my head, since ubuntu is telling you that line 54 is
messed up, I'd open the file in an editor (with superuser permissions)
and comment out line 54 just to get things running again. If you can see
what the mistake in line 54 is, all the better, as it can be quickly and
easily fixed. If you'd like to post your /etc/ap/sources.list file, I'd
be glad to post the fix to line 54.