Replace deprecated base::NonThreadSafe in components/signin in favor of SequenceChecker.

components/signin/core/browser/account_tracker_service.h

Index: components/signin/core/browser/account_tracker_service.h
diff --git a/components/signin/core/browser/account_tracker_service.h b/components/signin/core/browser/account_tracker_service.h
index b92e0a9515d1ad8c8992430a1570a599be8b8b2f..cc4035c4db41711c9395c5b5527c38164b903c7d 100644
--- a/components/signin/core/browser/account_tracker_service.h
+++ b/components/signin/core/browser/account_tracker_service.h
@@ -13,13 +13,12 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "base/timer/timer.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/signin/core/browser/account_info.h"
 #include "google_apis/gaia/gaia_auth_util.h"
 
-
 class PrefService;
 class SigninClient;
 
@@ -33,8 +32,7 @@ class PrefRegistrySyncable;
 
 // AccountTrackerService is a KeyedService that retrieves and caches GAIA
 // information about Google Accounts.
-class AccountTrackerService : public KeyedService,
-                              public base::NonThreadSafe {
+class AccountTrackerService : public KeyedService {
  public:
   // Name of the preference property that persists the account information
   // tracked by this service.
@@ -157,6 +155,8 @@ class AccountTrackerService : public KeyedService,
   std::map<std::string, AccountState> accounts_;
   base::ObserverList<Observer> observer_list_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(AccountTrackerService);
 };