sync: we can't lookup empty client tag nodes, so don't allow creating them

chrome/browser/sync/internal_api/write_node.cc

Index: chrome/browser/sync/internal_api/write_node.cc
diff --git a/chrome/browser/sync/internal_api/write_node.cc b/chrome/browser/sync/internal_api/write_node.cc
index 5dc7cc7adbc5881ce07b8d21ba2b0879eff7c228..3beeaf7a72eed287c4511568444e19871a6578c7 100644
--- a/chrome/browser/sync/internal_api/write_node.cc
+++ b/chrome/browser/sync/internal_api/write_node.cc
@@ -394,6 +394,10 @@ bool WriteNode::InitUniqueByCreation(syncable::ModelType model_type,
                                      const BaseNode& parent,
                                      const std::string& tag) {
   DCHECK(!entry_) << "Init called twice";
+  if (tag.empty()) {
+    LOG(WARNING) << "InitUniqueByCreation failed due to empty tag.";
+    return false;
+  }
 
   const std::string hash = GenerateSyncableHash(model_type, tag);