The basic setup is that Object (and now Array) Xrays apply various heuristics
to try to filter out dangerous properties from the underlying object. This
includes accessor properties, shadowing properties, callables, and non-Xrayable
objects. We need to make various fixes on the devtools side to keep this stuff
working.
Also, it would be nice if the tests were designed in such a way that a failed
string match didn't cause the whole test to hang without a useful error message.
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