Deprecate NonThreadSafe in components/sync in favor of SequenceChecker.

components/sync/engine/attachments/fake_attachment_downloader.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_ENGINE_ATTACHMENTS_FAKE_ATTACHMENT_DOWNLOADER_H_
 #define COMPONENTS_SYNC_ENGINE_ATTACHMENTS_FAKE_ATTACHMENT_DOWNLOADER_H_
 
 #include "base/macros.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "components/sync/engine/attachments/attachment_downloader.h"
 
 namespace syncer {
 
 // FakeAttachmentDownloader is for tests. For every request it posts a success
 // callback with empty attachment.
-class FakeAttachmentDownloader : public AttachmentDownloader,
-                                 public base::NonThreadSafe {
+class FakeAttachmentDownloader : public AttachmentDownloader {
  public:
   FakeAttachmentDownloader();
   ~FakeAttachmentDownloader() override;
 
   // AttachmentDownloader implementation.
   void DownloadAttachment(const AttachmentId& attachment_id,
                           const DownloadCallback& callback) override;
 
  private:
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(FakeAttachmentDownloader);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_ATTACHMENTS_FAKE_ATTACHMENT_DOWNLOADER_H_