`Istanbul-instrumenter-loader` has started to block updates to our other npm packages and is no longer being maintained.
`coverage-istanbul-loader` is pretty seamless but is stricter in regards to coverage for functions; I’ve opted to adjust the coverage requirements down for the affected files and file a followup to improve test coverage later.
Differential Revision: https://phabricator.services.mozilla.com/D175284
c65a4decdb