There's a browser-chrome test that does this, which means that _all_ subsequent
browser-chrome tests inherit it. So depending on the ordering of cases in
WrapperFactory, we might end up using a CrossCompartmentWrapper rather than an
XrayWrapper, meaning that stuff like nodePrincipal doesn't work anymore.
The semantics of UniversalXPConnect are now entirely dicatated by what makes
our test suite go green. So let's not force ourselves to bend over backwards
during wrapping to handle this case. And let's fix that stupid test while
we're at it.
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