Major Description
In FileTxnLog there is code that records the amount of time required to fsync the txn log in order to warn if that time exceeds a configurable threshold. This information should also be exported as a metric available by JMX so an important aspect of quorum performance can be monitored.
ZooKeeperServerMXBean carries some global latency information for the server process already, seems like a good place to put it if not an entirely new bean for the TxnLog. After ZOOKEEPER-2310 might want to collect the same information for snapshots.
