Log the sync communication that happens between client and server.

sync/protocol/proto_value_conversions.h

Index: sync/protocol/proto_value_conversions.h
diff --git a/sync/protocol/proto_value_conversions.h b/sync/protocol/proto_value_conversions.h
index 79bf1b1629baa80386930925cd648eb9cd907ac8..4fa8ca569c3d2985972e764809570eb7e327365d 100644
--- a/sync/protocol/proto_value_conversions.h
+++ b/sync/protocol/proto_value_conversions.h
@@ -20,6 +20,8 @@ class AppSpecifics;
 class AutofillProfileSpecifics;
 class AutofillSpecifics;
 class BookmarkSpecifics;
+class ClientToServerMessage;
+class ClientToServerResponse;
 class DeviceInformation;
 class EncryptedData;
 class EntitySpecifics;
@@ -137,6 +139,15 @@ base::DictionaryValue* TypedUrlSpecificsToValue(
 base::DictionaryValue* EntitySpecificsToValue(
     const sync_pb::EntitySpecifics& specifics);
 
+base::DictionaryValue* ClientToServerMessageToValue(
+    const sync_pb::ClientToServerMessage& proto,
+    bool include_specifics);
+
+base::DictionaryValue* ClientToServerResponseToValue(
+    const sync_pb::ClientToServerResponse& proto,
+    bool include_specifics);
+
+
 }  // namespace browser_sync
 
 #endif  // SYNC_PROTOCOL_PROTO_VALUE_CONVERSIONS_H_