Deprecate NonThreadSafe in components/sync in favor of SequenceChecker.

components/sync/engine/attachments/fake_attachment_downloader.cc

Index: components/sync/engine/attachments/fake_attachment_downloader.cc
diff --git a/components/sync/engine/attachments/fake_attachment_downloader.cc b/components/sync/engine/attachments/fake_attachment_downloader.cc
index 66f85fb7baadb19870e41fe9682fef76bf410976..767a58644c39b3cfdcf7291e57c0d620e2ffdd0d 100644
--- a/components/sync/engine/attachments/fake_attachment_downloader.cc
+++ b/components/sync/engine/attachments/fake_attachment_downloader.cc
@@ -18,13 +18,13 @@ namespace syncer {
 FakeAttachmentDownloader::FakeAttachmentDownloader() {}
 
 FakeAttachmentDownloader::~FakeAttachmentDownloader() {
-  DCHECK(CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 }
 
 void FakeAttachmentDownloader::DownloadAttachment(
     const AttachmentId& attachment_id,
     const DownloadCallback& callback) {
-  DCHECK(CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   // This is happy fake downloader, it always successfully downloads empty
   // attachment.
   scoped_refptr<base::RefCountedMemory> data(new base::RefCountedBytes());