[Sync] Store the past 10 traffic records in memory.

sync/engine/syncer_proto_util.cc

Index: sync/engine/syncer_proto_util.cc
diff --git a/sync/engine/syncer_proto_util.cc b/sync/engine/syncer_proto_util.cc
index 5051b82a02ee9753e7b9641608c77493123c7607..141c7e9343f463d771bde1583bf26a7afc33d400 100644
--- a/sync/engine/syncer_proto_util.cc
+++ b/sync/engine/syncer_proto_util.cc
@@ -339,6 +339,7 @@ SyncerError SyncerProtoUtil::PostClientToServerMessage(
   syncable::Directory* dir = session->context()->directory();
 
   LogClientToServerMessage(msg);
+  session->context()->traffic_recorder()->RecordClientToServerMessage(msg);
   if (!PostAndProcessHeaders(session->context()->connection_manager(), session,
                              msg, response)) {
     // There was an error establishing communication with the server.
@@ -353,6 +354,8 @@ SyncerError SyncerProtoUtil::PostClientToServerMessage(
   }
 
   LogClientToServerResponse(*response);
+  session->context()->traffic_recorder()->RecordClientToServerResponse(
+      *response);
 
   browser_sync::SyncProtocolError sync_protocol_error;