Summary:
This should make it easier to report errors, and also reduce codesize.
The reason this was so generic is that error reporting was unconditionally
enabled and was super-hot, but now that's no longer the case after bug 1452143,
so we can afford the virtual call in the "error reporting enabled" case.
This opens the possibility of simplifying a lot the error setup as well, though
this patch doesn't do it.
Test Plan: No behavior change, so no new tests.
Reviewers: xidorn
Bug #: 1469957
Differential Revision: https://phabricator.services.mozilla.com/D1734
MozReview-Commit-ID: F3wTdhX9MB5
4adea46644