Simple implementation

osu.Game/Beatmaps/BeatmapSetOnlineInfo.cs

@@ -66,6 +66,11 @@ namespace osu.Game.Beatmaps
         /// </summary>
         public int FavouriteCount { get; set; }
 
+        /// <summary>
+        /// Whether this beatmap set has been favourited by the current user.
+        /// </summary>
+        public bool HasFavourited { get; set; }
+
         /// <summary>
         /// The availability of this beatmap set.
         /// </summary>