new PingPong(pingId, sentTimestamp)
(Metric) A "holding struct" for pings and their experienced round-trip times - you may "subscribe" to ping results using MatsSocket#addPingPongListener(), and you may get the latest pings from the property MatsSocket#pings.
Sequence of the ping.
The experienced round-trip time for this ping-pong - this is the time back-and-forth. Note that this number can be a float, not necessarily integer.
Millis-from-epoch when this ping was sent.