Adding unit tests for PreviewsOptOutStoreSQL

components/previews/core/previews_black_list_item.h

Index: components/previews/core/previews_black_list_item.h
diff --git a/components/previews/core/previews_black_list_item.h b/components/previews/core/previews_black_list_item.h
index 462e61d1c4ade6782ada52f7035baef9dd35d5b2..03fa1b75c3a41bd1421803a4bca419c46f0fe123 100644
--- a/components/previews/core/previews_black_list_item.h
+++ b/components/previews/core/previews_black_list_item.h
@@ -37,20 +37,22 @@ class PreviewsBlackListItem {
   void AddPreviewNavigation(bool opt_out, base::Time entry_time);
 
   // Whether the host name corresponding to |this| should be disallowed from
   // showing previews.
   bool IsBlackListed(base::Time now) const;
 
   base::Optional<base::Time> most_recent_opt_out_time() const {
     return most_recent_opt_out_time_;
   }
 
+  size_t OptOutRecordsSizeForTesting() const;
+
  private:
   // A previews navigation to this host is represented by time and whether the
   // navigation was an opt out.
   struct OptOutRecord {
     OptOutRecord(base::Time entry_time, bool opt_out);
     ~OptOutRecord() {}
     const base::Time
         entry_time;      // The time that the opt out state was determined.
     const bool opt_out;  // Whether the user opt out of the preview.
   };