In some cases (unclear when), traceviewer-js, used by Lighthouse under the hood,
assumes `atob`/`btoa` are defined in the global scope. This is true for browser
environments, but not on node.
As a result, some aggregations that required access to model-tracing failed to
produce results, dropping the overall PWA score.
This affected #16665 (e.g. commit 0de6eec7a).