Setting the sync token here marks the memory store part as being
synced up to that point, but it isn't because the sync data hasn't
yet been injected into it.
The sync token will be set in the normal way when the cached sync
response is processed, at which point it will be accurate because
the cached sync data will actually have been processed by the sync
code and saved to the memory store.
David Baker
0594a8d03a