[Sync] Add HasChildren() function and use it instead of GetFirstChildId()

chrome/browser/sync/glue/bookmark_change_processor.cc

Index: chrome/browser/sync/glue/bookmark_change_processor.cc
diff --git a/chrome/browser/sync/glue/bookmark_change_processor.cc b/chrome/browser/sync/glue/bookmark_change_processor.cc
index 3735201ef0e52fad757710d9415bedf929c071fc..864f014dfc522b2d5549bced24255f15231eb456 100644
--- a/chrome/browser/sync/glue/bookmark_change_processor.cc
+++ b/chrome/browser/sync/glue/bookmark_change_processor.cc
@@ -90,7 +90,7 @@ void BookmarkChangeProcessor::RemoveOneSyncNode(
     return;
   }
   // This node should have no children.
-  DCHECK(sync_node.GetFirstChildId() == sync_api::kInvalidId);
+  DCHECK(!sync_node.HasChildren());
   // Remove association and delete the sync node.
   model_associator_->Disassociate(sync_node.GetId());
   sync_node.Remove();