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

chrome/browser/sync/glue/bookmark_model_associator.cc

Index: chrome/browser/sync/glue/bookmark_model_associator.cc
diff --git a/chrome/browser/sync/glue/bookmark_model_associator.cc b/chrome/browser/sync/glue/bookmark_model_associator.cc
index 720632cf91bab4c6961ba12ededd6f0aeb3fd69c..0e307c12fe8110102275fc47c291291cb9edcbe5 100644
--- a/chrome/browser/sync/glue/bookmark_model_associator.cc
+++ b/chrome/browser/sync/glue/bookmark_model_associator.cc
@@ -275,10 +275,9 @@ bool BookmarkModelAssociator::SyncModelHasUserCreatedNodes(bool* has_nodes) {
 
   // Sync model has user created nodes if either one of the permanent nodes
   // has children.
-  *has_nodes = bookmark_bar_node.GetFirstChildId() != sync_api::kInvalidId ||
-      other_bookmarks_node.GetFirstChildId() != sync_api::kInvalidId ||
-      (has_synced_folder &&
-          synced_bookmarks_node.GetFirstChildId() != sync_api::kInvalidId);
+  *has_nodes = bookmark_bar_node.HasChildren() ||
+      other_bookmarks_node.HasChildren() ||
+      (has_synced_folder && synced_bookmarks_node.HasChildren());
   return true;
 }