{
"type": "channel_history_changed",
"latest": "1358877455.000010",
"ts": "1361482916.000003",
"event_ts": "1361482916.000004"
}
A channel_history_changed event is sent to all clients in a channel when
bulk changes have occured to that channel's history. When clients receive this
message they should reload chat history for the channel if they have any
cached messages before latest.