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

components/reading_list/core/reading_list_model.h

Index: components/reading_list/core/reading_list_model.h
diff --git a/components/reading_list/core/reading_list_model.h b/components/reading_list/core/reading_list_model.h
index d0031588b7f245fc6b37a1a5a0f4c183847a5322..c51e01613285971f7aaa1eddd1e9b4b1df472b98 100644
--- a/components/reading_list/core/reading_list_model.h
+++ b/components/reading_list/core/reading_list_model.h
@@ -11,7 +11,7 @@
 
 #include "base/callback.h"
 #include "base/observer_list.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "components/reading_list/core/reading_list_entry.h"
 #include "components/reading_list/core/reading_list_model_observer.h"
 
@@ -27,7 +27,7 @@ class ModelTypeSyncBridge;
 // other of read ones. This object should only be accessed from one thread
 // (Usually the main thread). The observers callbacks are also sent on the main
 // thread.
-class ReadingListModel : public base::NonThreadSafe {
+class ReadingListModel {
  public:
   class ScopedReadingListBatchUpdate;
 
@@ -170,6 +170,8 @@ class ReadingListModel : public base::NonThreadSafe {
   // Called when model is leaving batch update mode.
   virtual void LeavingBatchUpdates();
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
  private:
   unsigned int current_batch_updates_count_;