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

components/sync/syncable/write_node.h

 // Copyright 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_WRITE_NODE_H_
 #define COMPONENTS_SYNC_SYNCABLE_WRITE_NODE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 47 matching lines @@
 
   // A client must use one (and only one) of the following Init variants to
   // populate the node.
 
   // BaseNode implementation.
   InitByLookupResult InitByIdLookup(int64_t id) override;
   InitByLookupResult InitByClientTagLookup(ModelType model_type,
                                            const std::string& tag) override;
 
   // Create a new bookmark node with the specified parent and predecessor.  Use
-  // a NULL |predecessor| to indicate that this is to be the first child.
-  // |predecessor| must be a child of |new_parent| or NULL. Returns false on
+  // a null |predecessor| to indicate that this is to be the first child.
+  // |predecessor| must be a child of |new_parent| or null. Returns false on
   // failure.
   bool InitBookmarkByCreation(const BaseNode& parent,
                               const BaseNode* predecessor);
 
   // Create nodes using this function if they're unique items that
   // you want to fetch using client_tag. Note that the behavior of these
   // items is slightly different than that of normal items.
   // Most importantly, if it exists locally but is deleted, this function will
   // actually undelete it. Otherwise it will reuse the existing node.
   // Client unique tagged nodes must NOT be folders.
@@ skipping 23 matching lines @@
 
   // Remove this node and its children and sync deletion to server.
   void Tombstone();
 
   // If the node is known by server, remove it and its children but don't sync
   // deletion to server. Do nothing if the node is not known by server so that
   // server can have a record of the node.
   void Drop();
 
   // Set a new parent and position.  Position is specified by |predecessor|; if
-  // it is NULL, the node is moved to the first position.  |predecessor| must
-  // be a child of |new_parent| or NULL.  Returns false on failure..
+  // it is null, the node is moved to the first position.  |predecessor| must
+  // be a child of |new_parent| or null.  Returns false on failure..
   bool SetPosition(const BaseNode& new_parent, const BaseNode* predecessor);
 
   // Set the bookmark specifics (url and favicon).
   // Should only be called if GetModelType() == BOOKMARK.
   void SetBookmarkSpecifics(const sync_pb::BookmarkSpecifics& specifics);
 
   // Generic set specifics method. Will extract the model type from |specifics|.
   void SetEntitySpecifics(const sync_pb::EntitySpecifics& specifics);
 
   // Resets the EntitySpecifics for this node based on the unencrypted data.
@@ skipping 48 matching lines @@
 
   // The sync API transaction that is the parent of this node.
   WriteTransaction* transaction_;
 
   DISALLOW_COPY_AND_ASSIGN(WriteNode);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_SYNCABLE_WRITE_NODE_H_