Convert //sync from scoped_ptr to std::unique_ptr

sync/syncable/directory_backing_store.h

Index: sync/syncable/directory_backing_store.h
diff --git a/sync/syncable/directory_backing_store.h b/sync/syncable/directory_backing_store.h
index 50fba9c88347cf48fbb166bd24b91d26f37ded8c..a2c8d9cc80bcfa7d92f13cf9e24ec92572173b2a 100644
--- a/sync/syncable/directory_backing_store.h
+++ b/sync/syncable/directory_backing_store.h
@@ -7,11 +7,11 @@
 
 #include <stdint.h>
 
+#include <memory>
 #include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "sql/connection.h"
 #include "sql/statement.h"
@@ -249,7 +249,7 @@ class SYNC_EXPORT DirectoryBackingStore : public base::NonThreadSafe {
   const std::string dir_name_;
   const int database_page_size_;
 
-  scoped_ptr<sql::Connection> db_;
+  std::unique_ptr<sql::Connection> db_;
   sql::Statement save_meta_statement_;
   sql::Statement save_delete_journal_statement_;