This is a continuation of 68fd102, which did the same thing but only for
StopInfo. Using make_shared is both safer and more efficient:
- With make_shared, the object and the control block are allocated
together, which is more efficient.
- With make_shared, the enable_shared_from_this base class is properly
linked to the control block before the constructor finishes, so
shared_from_this() will be safe to use (though still not recommended
during construction).
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