Currently this isn't a security problem, because jsids in the tree are either primitives or atoms, neither of which are relevant for the GC. However, once we start implementing ES6 symbols, jsids will start being objects as well. So we should be safe and fix this, even though it's likely that we'll remove XPCWrappedNativeXrayTraits::enumerateNames before we land symbols.

Green try run: https://tbpl.mozilla.org/?tree=Try&rev=7a14732b3cb2

Green try push: https://tbpl.mozilla.org/?tree=Try&rev=7a14732b3cb2 remote: https://hg.mozilla.org/integration/mozilla-inbound/rev/ac0114b94488