Deprecate NonThreadSafe in components/sync in favor of SequenceChecker.

components/sync/engine_impl/attachments/attachment_downloader_impl_unittest.cc

Index: components/sync/engine_impl/attachments/attachment_downloader_impl_unittest.cc
diff --git a/components/sync/engine_impl/attachments/attachment_downloader_impl_unittest.cc b/components/sync/engine_impl/attachments/attachment_downloader_impl_unittest.cc
index 5c8013067b7da9054cef784c265dbccb04d5cc15..5a3c42a65a62ca05427f0f53a74bb0e834e6ad29 100644
--- a/components/sync/engine_impl/attachments/attachment_downloader_impl_unittest.cc
+++ b/components/sync/engine_impl/attachments/attachment_downloader_impl_unittest.cc
@@ -13,6 +13,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
+#include "base/sequence_checker.h"
 #include "base/single_thread_task_runner.h"
 #include "base/test/histogram_tester.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ -105,8 +106,7 @@ void MockOAuth2TokenService::InvalidateAccessTokenImpl(
 }
 
 class TokenServiceProvider
-    : public OAuth2TokenServiceRequest::TokenServiceProvider,
-      base::NonThreadSafe {
+    : public OAuth2TokenServiceRequest::TokenServiceProvider {
  public:
   explicit TokenServiceProvider(OAuth2TokenService* token_service);
 
@@ -120,6 +120,8 @@ class TokenServiceProvider
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
   OAuth2TokenService* token_service_;
+
+  SEQUENCE_CHECKER(sequence_checker_);
 };
 
 TokenServiceProvider::TokenServiceProvider(OAuth2TokenService* token_service)
@@ -128,7 +130,9 @@ TokenServiceProvider::TokenServiceProvider(OAuth2TokenService* token_service)
   DCHECK(token_service_);
 }
 
-TokenServiceProvider::~TokenServiceProvider() {}
+TokenServiceProvider::~TokenServiceProvider() {
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+}
 
 scoped_refptr<base::SingleThreadTaskRunner>
 TokenServiceProvider::GetTokenServiceTaskRunner() {