This interface is provided for testing purposes only, basically
just to solve link vagaries. See docs in StartupCache.h
GetBuffer, PutBuffer, and InvalidateCache act as described
in that file. */
In debug builds, wraps this object output stream with a stream that will
detect and prevent the write of a multiply-referenced non-singleton object
during serialization. In non-debug, returns an add-ref’d pointer to
original stream, unwrapped. */