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

components/prefs/json_pref_store.h

Index: components/prefs/json_pref_store.h
diff --git a/components/prefs/json_pref_store.h b/components/prefs/json_pref_store.h
index b298d30e6915cfa68a12dcd5bf5d6f6b0bfcef5f..90fde73064ee5b2eb68bf26498d3cb05e0096f6a 100644
--- a/components/prefs/json_pref_store.h
+++ b/components/prefs/json_pref_store.h
@@ -19,8 +19,8 @@
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
+#include "base/sequence_checker.h"
 #include "base/task_scheduler/post_task.h"
-#include "base/threading/non_thread_safe.h"
 #include "components/prefs/base_prefs_export.h"
 #include "components/prefs/persistent_pref_store.h"
 #include "components/prefs/pref_filter.h"
@@ -48,8 +48,7 @@ FORWARD_DECLARE_TEST(JsonPrefStoreTest, WriteCountHistogramTestPeriodWithGaps);
 class COMPONENTS_PREFS_EXPORT JsonPrefStore
     : public PersistentPrefStore,
       public base::ImportantFileWriter::DataSerializer,
-      public base::SupportsWeakPtr<JsonPrefStore>,
-      public base::NonThreadSafe {
+      public base::SupportsWeakPtr<JsonPrefStore> {
  public:
   struct ReadResult;
 
@@ -253,6 +252,8 @@ class COMPONENTS_PREFS_EXPORT JsonPrefStore
 
   WriteCountHistogram write_count_histogram_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(JsonPrefStore);
 };