Implement a bag of chips for sync.

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 8149ad8e5301500f0c3044e2d4acc97cf3323854..4fb0b17a3167756fde9c6b3bdb611563e160f8f0 100644
--- a/sync/engine/syncer_proto_util.cc
+++ b/sync/engine/syncer_proto_util.cc
@@ -163,6 +163,12 @@ void SyncerProtoUtil::AddRequestBirthday(syncable::Directory* dir,
 }
 
 // static
+void SyncerProtoUtil::AddBagOfChips(syncable::Directory* dir,
+                                    ClientToServerMessage* msg) {
+  msg->mutable_bag_of_chips()->ParseFromString(dir->bag_of_chips());
+}
+
+// static
 void SyncerProtoUtil::SetProtocolVersion(ClientToServerMessage* msg) {
   const int current_version =
       ClientToServerMessage::default_instance().protocol_version();
@@ -243,6 +249,7 @@ namespace {
 
 // Helper function for an assertion in PostClientToServerMessage.
 bool IsVeryFirstGetUpdates(const ClientToServerMessage& message) {
+  DCHECK(message.has_bag_of_chips());
   if (!message.has_get_updates())
     return false;
   DCHECK_LT(0, message.get_updates().from_progress_marker_size());
@@ -509,6 +516,16 @@ const std::string& SyncerProtoUtil::NameFromCommitEntryResponse(
   return entry.name();
 }
 
+// static
+void SyncerProtoUtil::PersistBagOfChips(syncable::Directory* dir,
+    const sync_pb::ClientToServerResponse& response) {
+  if (!response.has_new_bag_of_chips())
+    return;
+  std::string bag_of_chips;
+  if (response.new_bag_of_chips().SerializeToString(&bag_of_chips))
+    dir->set_bag_of_chips(bag_of_chips);
+}
+
 std::string SyncerProtoUtil::SyncEntityDebugString(
     const sync_pb::SyncEntity& entry) {
   const std::string& mtime_str =