[Sync] Replacing NULL with nullptr in code and null in comments for components/sync/

components/sync/syncable/parent_child_index.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_SYNC_SYNCABLE_PARENT_CHILD_INDEX_H_
 #define COMPONENTS_SYNC_SYNCABLE_PARENT_CHILD_INDEX_H_
 
 #include <map>
 #include <memory>
 #include <set>
@@ skipping 31 matching lines @@
 
   // Inserts a given child into the index.
   bool Insert(EntryKernel* e);
 
   // Removes a given child from the index.
   void Remove(EntryKernel* e);
 
   // Returns true if this item is in the index as a child.
   bool Contains(EntryKernel* e) const;
 
-  // Returns all children of the entry with the given Id.  Returns NULL if the
+  // Returns all children of the entry with the given Id.  Returns null if the
   // node has no children or the Id does not identify a valid directory node.
   const OrderedChildSet* GetChildren(const Id& id) const;
 
-  // Returns all children of the entry.  Returns NULL if the node has no
+  // Returns all children of the entry.  Returns null if the node has no
   // children.
   const OrderedChildSet* GetChildren(EntryKernel* e) const;
 
   // Returns all siblings of the entry.
   const OrderedChildSet* GetSiblings(EntryKernel* e) const;
 
  private:
   friend class ParentChildIndexTest;
 
   typedef std::map<Id, OrderedChildSetRef> ParentChildrenMap;
@@ skipping 28 matching lines @@
   // with implicit parent.
   TypeRootChildSets type_root_child_sets_;
 
   DISALLOW_COPY_AND_ASSIGN(ParentChildIndex);
 };
 
 }  // namespace syncable
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_SYNCABLE_PARENT_CHILD_INDEX_H_