Deprecate NonThreadSafe in components/sync in favor of SequenceChecker.

components/sync/syncable/directory_backing_store.h

Index: components/sync/syncable/directory_backing_store.h
diff --git a/components/sync/syncable/directory_backing_store.h b/components/sync/syncable/directory_backing_store.h
index b50f2dfb2d1887064aca17712271e3745a5d6897..149a32ff65e217e56e122e6ab6b2652203392297 100644
--- a/components/sync/syncable/directory_backing_store.h
+++ b/components/sync/syncable/directory_backing_store.h
@@ -12,7 +12,7 @@
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/syncable/dir_open_result.h"
 #include "components/sync/syncable/directory.h"
@@ -51,7 +51,7 @@ extern const int32_t kCurrentPageSizeKB;
 // This class is abstract so that we can extend it in interesting ways for use
 // in tests.  The concrete class used in non-test scenarios is
 // OnDiskDirectoryBackingStore.
-class DirectoryBackingStore : public base::NonThreadSafe {
+class DirectoryBackingStore {
  public:
   explicit DirectoryBackingStore(const std::string& dir_name);
   virtual ~DirectoryBackingStore();
@@ -195,6 +195,8 @@ class DirectoryBackingStore : public base::NonThreadSafe {
   // Destroys the existing Connection and creates a new one.
   void ResetAndCreateConnection();
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
  private:
   friend class DirectoryBackingStoreTest;
   friend class TestDirectoryBackingStore;