Implement a bag of chips for sync.

sync/engine/store_timestamps_command.cc

Index: sync/engine/store_timestamps_command.cc
diff --git a/sync/engine/store_timestamps_command.cc b/sync/engine/store_timestamps_command.cc
index bab995e7a99ce830607fabf324245874bed17349..d13f4a18b30b4ba686543abc55593581038d9c94 100644
--- a/sync/engine/store_timestamps_command.cc
+++ b/sync/engine/store_timestamps_command.cc
@@ -4,6 +4,7 @@
 
 #include "sync/engine/store_timestamps_command.h"
 
+#include "sync/engine/syncer_proto_util.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/sessions/status_controller.h"
 #include "sync/sessions/sync_session.h"
@@ -18,11 +19,15 @@ SyncerError StoreTimestampsCommand::ExecuteImpl(
     sessions::SyncSession* session) {
   syncable::Directory* dir = session->context()->directory();
 
-  const sync_pb::GetUpdatesResponse& updates =
-      session->status_controller().updates_response().get_updates();
+  const sync_pb::ClientToServerResponse& response =
+      session->status_controller().updates_response();
+  const sync_pb::GetUpdatesResponse& updates = response.get_updates();
 
   sessions::StatusController* status = session->mutable_status_controller();
 
+  // Persist a bag of chips if it has been sent by the server.
+  SyncerProtoUtil::PersistBagOfChips(dir, response);
+
   // Update the progress marker tokens from the server result.  If a marker
   // was omitted for any one type, that indicates no change from the previous
   // state.