sfink pointed out in #spidermonkey that [we actually use at least one of those bits](https://searchfox.org/mozilla-central/rev/f9beb753a84aa297713d1565dcd0c5e3c66e4174/js/public/TraceKind.h#47,67-68).
Bug 1231541 Comment 3 Edit History
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~~sfink pointed out in #spidermonkey that [we actually use at least one of those bits](https://searchfox.org/mozilla-central/rev/f9beb753a84aa297713d1565dcd0c5e3c66e4174/js/public/TraceKind.h#47,67-68).~~ Never mind, we were misreading the code. Those bits live elsewhere.