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

components/sync/syncable/directory_backing_store_unittest.cc

 // 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.
 
 #include "components/sync/syncable/directory_backing_store.h"
 
 #include <stddef.h>
 
 #include <map>
 
@@ skipping 23 matching lines @@
 void CatastrophicErrorHandler(bool* catastrophic_error_handler_was_called) {
   *catastrophic_error_handler_was_called = true;
 }
 
 // Create a dirty EntryKernel with an ID derived from |id| + |id_suffix|.
 std::unique_ptr<EntryKernel> CreateEntry(int id, const std::string& id_suffix) {
   std::unique_ptr<EntryKernel> entry(new EntryKernel());
   std::string id_string = base::Int64ToString(id) + id_suffix;
   entry->put(ID, Id::CreateFromClientString(id_string));
   entry->put(META_HANDLE, id);
-  entry->mark_dirty(NULL);
+  entry->mark_dirty(nullptr);
   return entry;
 }
 
 }  // namespace
 
 extern const int32_t kCurrentPageSizeKB;
 extern const int32_t kCurrentDBVersion;
 
 class MigrationTest : public testing::TestWithParam<int> {
  public:
@@ skipping 4256 matching lines @@
   ASSERT_FALSE(dbs->SaveChanges(snapshot));
   // At this point the handler has been posted but not executed.
   ASSERT_FALSE(was_called);
   // Pump the message loop and see that it is executed.
   base::RunLoop().RunUntilIdle();
   ASSERT_TRUE(was_called);
 }
 
 }  // namespace syncable
 }  // namespace syncer