[Sync::USS] Don't populate client_defined_unique_tag for bookmarks

The server identifies bookmark commit requests by the absence of a
client_defined_unique_tag.
Bookmarks should be handled differently when generating server ids.

This CL makes sure the client_defined_unique_tag is only populated
for non-bookmark data types.

Bug: 516866
Change-Id: I0c3b1f314c638878fd8780663484aec780215e99
Reviewed-on: https://chromium-review.googlesource.com/1169052
Commit-Queue: Mohamed Amir Yosef <mamir@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581878}

components/sync/engine_impl/non_blocking_type_commit_contribution.cc

@@ -173,7 +173,10 @@ void NonBlockingTypeCommitContribution::PopulateCommitProto(
     sync_pb::SyncEntity* commit_proto) {
   const EntityData& entity_data = commit_entity.entity.value();
   commit_proto->set_id_string(entity_data.id);
-  commit_proto->set_client_defined_unique_tag(entity_data.client_tag_hash);
+  // Populate client_defined_unique_tag only for non-bookmark data types.
+  if (!entity_data.specifics.has_bookmark()) {
+    commit_proto->set_client_defined_unique_tag(entity_data.client_tag_hash);
+  }
   commit_proto->set_version(commit_entity.base_version);
   commit_proto->set_deleted(entity_data.is_deleted());
   commit_proto->set_folder(entity_data.is_folder);