Cross-referencing angular/angular.js#7663

Basically, we do this already for function paramters, it needs to happen for JSON values too.

In fact, if a JSON literal expression contains non-const expressions, then most likely we should exclusively be watching the subexpressions, and not the JSON object itself --- so that we don't end up replacing the whole object and creating garbage.

We already do this for PureFunctionAST (and I don't think this should be removed as cargo cult), so we ought to do it for JSON literal properties too. I can't recall if we're already doing that, but I don't believe we have tests for it. I'll check