Enable Null Syncable ID which is different than Root ID.

sync/syncable/nigori_util.cc

Index: sync/syncable/nigori_util.cc
diff --git a/sync/syncable/nigori_util.cc b/sync/syncable/nigori_util.cc
index 2731e7fbbd9132aebcd863b1b6016f34ac958918..b43acfaef1959619c475df824e7247c117bf0440 100644
--- a/sync/syncable/nigori_util.cc
+++ b/sync/syncable/nigori_util.cc
@@ -112,7 +112,7 @@ bool VerifyDataTypeEncryptionForTest(
   while (!to_visit.empty()) {
     id_string = to_visit.front();
     to_visit.pop();
-    if (id_string.IsRoot())
+    if (id_string.IsNull())
       continue;
 
     Entry child(trans, GET_BY_ID, id_string);