[Sync] Replace typedef with using.

components/sync/syncable/parent_child_index.h

Index: components/sync/syncable/parent_child_index.h
diff --git a/components/sync/syncable/parent_child_index.h b/components/sync/syncable/parent_child_index.h
index b5af56b265b70c1e1907904bd92e23175ff40110..48ff0b476e0a54c4d9fcee99599d9e52af374837 100644
--- a/components/sync/syncable/parent_child_index.h
+++ b/components/sync/syncable/parent_child_index.h
@@ -26,8 +26,8 @@ struct ChildComparator {
 };
 
 // An ordered set of nodes.
-typedef std::set<EntryKernel*, ChildComparator> OrderedChildSet;
-typedef std::shared_ptr<OrderedChildSet> OrderedChildSetRef;
+using OrderedChildSet = std::set<EntryKernel*, ChildComparator>;
+using OrderedChildSetRef = std::shared_ptr<OrderedChildSet>;
 
 // Container that tracks parent-child relationships.
 // Provides fast lookup of all items under a given parent.
@@ -66,9 +66,9 @@ class ParentChildIndex {
  private:
   friend class ParentChildIndexTest;
 
-  typedef std::map<Id, OrderedChildSetRef> ParentChildrenMap;
-  typedef std::vector<Id> TypeRootIds;
-  typedef std::vector<OrderedChildSetRef> TypeRootChildSets;
+  using ParentChildrenMap = std::map<Id, OrderedChildSetRef>;
+  using TypeRootIds = std::vector<Id>;
+  using TypeRootChildSets = std::vector<OrderedChildSetRef>;
 
   static bool ShouldUseParentId(const Id& parent_id, ModelType model_type);