Replace deprecated base::NonThreadSafe in base in favor of SequenceChecker.

base/files/important_file_writer.h

Index: base/files/important_file_writer.h
diff --git a/base/files/important_file_writer.h b/base/files/important_file_writer.h
index 46efbaa145c2cf4c683c64b4f5fda6765da81f57..5fcd5153c28ae49830760b7ef9aec19aca4479cb 100644
--- a/base/files/important_file_writer.h
+++ b/base/files/important_file_writer.h
@@ -12,8 +12,8 @@
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/sequence_checker.h"
 #include "base/strings/string_piece.h"
-#include "base/threading/non_thread_safe.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 
@@ -35,7 +35,7 @@ class SequencedTaskRunner;
 //
 // Also note that ImportantFileWriter can be *really* slow (cf. File::Flush()
 // for details) and thus please don't block shutdown on ImportantFileWriter.
-class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
+class BASE_EXPORT ImportantFileWriter {
  public:
   // Used by ScheduleSave to lazily provide the data to be saved. Allows us
   // to also batch data serializations.
@@ -143,6 +143,8 @@ class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
   // Time delta after which scheduled data will be written to disk.
   const TimeDelta commit_interval_;
 
+  SEQUENCE_CHECKER(sequence_checker_);
+
   WeakPtrFactory<ImportantFileWriter> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ImportantFileWriter);