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

components/sync/driver/model_associator.h

 // Copyright 2014 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_DRIVER_MODEL_ASSOCIATOR_H_
 #define COMPONENTS_SYNC_DRIVER_MODEL_ASSOCIATOR_H_
 
 #include <stdint.h>
 
 #include "base/synchronization/lock.h"
@@ skipping 53 matching lines @@
 template <class Node, class IDType>
 class PerDataTypeAssociatorInterface : public AssociatorInterface {
  public:
   virtual ~PerDataTypeAssociatorInterface() {}
   // Returns sync id for the given chrome model id.
   // Returns kInvalidId if the sync node is not found for the given
   // chrome id.
   virtual int64_t GetSyncIdFromChromeId(const IDType& id) = 0;
 
   // Returns the chrome node for the given sync id.
-  // Returns NULL if no node is found for the given sync id.
+  // Returns null if no node is found for the given sync id.
   virtual const Node* GetChromeNodeFromSyncId(int64_t sync_id) = 0;
 
   // Initializes the given sync node from the given chrome node id.
   // Returns false if no sync node was found for the given chrome node id or
   // if the initialization of sync node fails.
   virtual bool InitSyncNodeFromChromeId(const IDType& node_id,
                                         BaseNode* sync_node) = 0;
 
   // Associates the given chrome node with the given sync node.
   virtual void Associate(const Node* node, const BaseNode& sync_node) = 0;
 
   // Remove the association that corresponds to the given sync id.
   virtual void Disassociate(int64_t sync_id) = 0;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_DRIVER_MODEL_ASSOCIATOR_H_