sync: Set explicit protocol_version on commit

sync/engine/commit.cc

Index: sync/engine/commit.cc
diff --git a/sync/engine/commit.cc b/sync/engine/commit.cc
index f9a56e900d976962f2180e5bea5b336faac9b46e..4da658dda2734b8e82ee08180dc247bad0dd79ed 100644
--- a/sync/engine/commit.cc
+++ b/sync/engine/commit.cc
@@ -70,6 +70,9 @@ bool PrepareCommitMessage(sessions::SyncSession* session,
   commit_set->Clear();
   commit_message->Clear();
 
+  // TODO(134769): This is a temporary fix for crbug.com/134715.
+  commit_message->set_protocol_version(commit_message->protocol_version());
+
   WriteTransaction trans(FROM_HERE, SYNCER, session->context()->directory());
   sessions::ScopedSetSessionWriteTransaction set_trans(session, &trans);