[USS] Fix a hack for populating missing wallet_data client tags

This CL deals properly with the root node for wallet data. This node
is sent (at least) in integration tests for migration to USS.

Bug: 853688
Change-Id: I94f38e38a4f7db7a7e960e5205c64d7ad6cf49e7
Reviewed-on: https://chromium-review.googlesource.com/1238541
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593188}

components/sync/model_impl/client_tag_based_model_type_processor.cc

@@ -603,12 +603,18 @@ void ClientTagBasedModelTypeProcessor::OnCommitCompleted(
 
 // Returns an updates list that has client tag hashes populated for every
 // update entity.
-UpdateResponseDataList PopulateClientTags(
+UpdateResponseDataList PopulateClientTagsForWalletData(
     const ModelType& type,
     ModelTypeSyncBridge* bridge,
     const UpdateResponseDataList& updates) {
   UpdateResponseDataList updates_with_client_tags;
   for (const UpdateResponseData& update : updates) {
+    if (update.entity->parent_id == "0") {
+      // Ignore the permanent root node. Other places in this file detect them
+      // by having empty client tags; this cannot be used for wallet_data as no
+      // wallet_data entity has a client tag.
+      continue;
+    }
     updates_with_client_tags.push_back(update);
     updates_with_client_tags.back().entity =
         update.entity->UpdateClientTagHash(GenerateSyncableHash(
@@ -646,7 +652,8 @@ void ClientTagBasedModelTypeProcessor::OnUpdateReceived(
     // fully use client tags, or to use a different processor.
     // TODO(crbug.com/874001): Remove this feature-specific logic when the right
     // solution for Wallet data has been decided.
-    pre_processed_updates = PopulateClientTags(type_, bridge_, updates);
+    pre_processed_updates =
+        PopulateClientTagsForWalletData(type_, bridge_, updates);
     updates_to_process = &pre_processed_updates;
   }