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

components/prefs/pref_service.h

Index: components/prefs/pref_service.h
diff --git a/components/prefs/pref_service.h b/components/prefs/pref_service.h
index a360afa44acccffed83987110e086ae7c2ff70fd..8b3371708247b14c0c71f4bf5d6fde80c130acab 100644
--- a/components/prefs/pref_service.h
+++ b/components/prefs/pref_service.h
@@ -23,7 +23,7 @@
 #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/values.h"
 #include "components/prefs/base_prefs_export.h"
 #include "components/prefs/persistent_pref_store.h"
@@ -55,7 +55,7 @@ class ScopedUserPrefUpdateBase;
 // Settings and storage accessed through this class represent
 // user-selected preferences and information and MUST not be
 // extracted, overwritten or modified except through the defined APIs.
-class COMPONENTS_PREFS_EXPORT PrefService : public base::NonThreadSafe {
+class COMPONENTS_PREFS_EXPORT PrefService {
  public:
   enum PrefInitializationStatus {
     INITIALIZATION_STATUS_WAITING,
@@ -397,6 +397,8 @@ class COMPONENTS_PREFS_EXPORT PrefService : public base::NonThreadSafe {
   // of registered preferences are.
   mutable PreferenceMap prefs_map_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(PrefService);
 };