[Sync] Replacing NULL with nullptr/null throughout sync code.

components/sync_bookmarks/bookmark_model_associator.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_BOOKMARKS_BOOKMARK_MODEL_ASSOCIATOR_H_
 #define COMPONENTS_SYNC_BOOKMARKS_BOOKMARK_MODEL_ASSOCIATOR_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 70 matching lines @@
   // The has_nodes out param is true if the sync model has nodes other
   // than the permanent tagged nodes.
   bool SyncModelHasUserCreatedNodes(bool* has_nodes) override;
 
   // Returns sync id for the given bookmark node id.
   // Returns syncer::kInvalidId if the sync node is not found for the given
   // bookmark node id.
   int64_t GetSyncIdFromChromeId(const int64_t& node_id) override;
 
   // Returns the bookmark node for the given sync id.
-  // Returns NULL if no bookmark node is found for the given sync id.
+  // Returns null if no bookmark node is found for the given sync id.
   const bookmarks::BookmarkNode* GetChromeNodeFromSyncId(
       int64_t sync_id) override;
 
   // Initializes the given sync node from the given bookmark node id.
   // Returns false if no sync node was found for the given bookmark node id or
   // if the initialization of sync node fails.
   bool InitSyncNodeFromChromeId(const int64_t& node_id,
                                 syncer::BaseNode* sync_node) override;
 
   // Associates the given bookmark node with the given sync node.
@@ skipping 201 matching lines @@
   // guarantees no invocations can occur if |this| has been deleted. (This
   // allows this class to be non-refcounted).
   base::WeakPtrFactory<BookmarkModelAssociator> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BookmarkModelAssociator);
 };
 
 }  // namespace sync_bookmarks
 
 #endif  // COMPONENTS_SYNC_BOOKMARKS_BOOKMARK_MODEL_ASSOCIATOR_H_