Log the sync communication that happens between client and server.

chrome/browser/sync/engine/syncer_proto_util.cc

Index: chrome/browser/sync/engine/syncer_proto_util.cc
diff --git a/chrome/browser/sync/engine/syncer_proto_util.cc b/chrome/browser/sync/engine/syncer_proto_util.cc
index e2e235b30328c8389f63dd11bd1d7acb9e5b8e54..fbb272e6b8a9aee49faa6707facefefe4c73d804 100644
--- a/chrome/browser/sync/engine/syncer_proto_util.cc
+++ b/chrome/browser/sync/engine/syncer_proto_util.cc
@@ -5,10 +5,13 @@
 #include "chrome/browser/sync/engine/syncer_proto_util.h"
 
 #include "base/format_macros.h"
+#include "base/json/json_writer.h"
 #include "base/stringprintf.h"
 #include "chrome/browser/sync/engine/net/server_connection_manager.h"
 #include "chrome/browser/sync/engine/syncer.h"
 #include "chrome/browser/sync/engine/syncer_types.h"
+#include "chrome/browser/sync/engine/traffic_logger.h"
+#include "chrome/browser/sync/protocol/proto_value_conversions.h"
 #include "chrome/browser/sync/protocol/service_constants.h"
 #include "chrome/browser/sync/protocol/sync_protocol_error.h"
 #include "chrome/browser/sync/sessions/sync_session.h"
@@ -337,6 +340,7 @@ SyncerError SyncerProtoUtil::PostClientToServerMessage(
 
   syncable::Directory* dir = session->context()->directory();
 
+  LogClientToServerMessage(msg);
   if (!PostAndProcessHeaders(session->context()->connection_manager(), session,
                              msg, response)) {
     // There was an error establishing communication with the server.
@@ -350,6 +354,8 @@ SyncerError SyncerProtoUtil::PostClientToServerMessage(
     return ServerConnectionErrorAsSyncerError(server_status);
   }
 
+  LogClientToServerResponse(*response);
+
   browser_sync::SyncProtocolError sync_protocol_error;
 
   // Birthday mismatch overrides any error that is sent by the server.