There was no real code sharing going on here and instead due to the size of
ElementCollector made it difficult to ascertain without reading the code that
the two code paths are completely separate.
This is a NFC change internal to DIMemoryUseCollector that is not visible
outside of DI.
rdar://31521023
This is necessary since other passes rely on DIMemoryUseCollector.h and I want
to update each one of them individually to minimize disruption.
rdar://31521023