sync: In ChronoChat2013, add a MemoryContentCache. In onInterest, add the interest to a local pendingInterestTable_. Add the private method contentCacheAdd, and when we add a data packet, try to satisfy any interest in the pendingInterestTable_. In broadcastSyncState, use contentCacheAdd instead of poking to the transport. Now we can remove transport from the constructor.
tests: In test-chrono-chat, now we don't need to send transport to the ChronoChat2013 constructor.