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

components/browser_sync/test_profile_sync_service.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_BROWSER_SYNC_TEST_PROFILE_SYNC_SERVICE_H_
 #define COMPONENTS_BROWSER_SYNC_TEST_PROFILE_SYNC_SERVICE_H_
 
 #include "base/macros.h"
 #include "components/browser_sync/profile_sync_service.h"
 #include "components/sync/base/weak_handle.h"
@@ skipping 20 matching lines @@
   syncer::UserShare* GetUserShare() const override;
 
   syncer::TestIdFactory* id_factory();
 
   // Raise visibility to ease testing.
   using ProfileSyncService::NotifyObservers;
 
   syncer::SyncPrefs* sync_prefs() { return &sync_prefs_; }
 
  protected:
-  // Return NULL handle to use in backend initialization to avoid receiving
+  // Return null handle to use in backend initialization to avoid receiving
   // js messages on UI loop when it's being destroyed, which are not deleted
   // and cause memory leak in test.
   syncer::WeakHandle<syncer::JsEventHandler> GetJsEventHandler() override;
 
  private:
   syncer::TestIdFactory id_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TestProfileSyncService);
 };
 
 }  // namespace browser_sync
 
 #endif  // COMPONENTS_BROWSER_SYNC_TEST_PROFILE_SYNC_SERVICE_H_