Added new request for getting the beatmapset from only a difficulty map ID

osu.Game/Online/API/Requests/GetBeatmapRequest.cs

@@ -0,0 +1,21 @@
+using osu.Game.Beatmaps;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace osu.Game.Online.API.Requests
+{
+    public class GetBeatmapRequest : APIRequest<BeatmapInfo>
+    {
+        private readonly int beatmapId;
+
+        public GetBeatmapRequest(int beatmapId)
+        {
+            this.beatmapId = beatmapId;
+        }
+
+        protected override string Target => $@"beatmaps/{beatmapId}";
+    }
+}

osu.Game/Overlays/BeatmapSetOverlay.cs

@@ -139,6 +139,20 @@ namespace osu.Game.Overlays
             return true;
         }
 
+        public void ShowBeatmap(int beatmapId)
+        {
+            var req = new GetBeatmapRequest(beatmapId);
+            req.Success += res =>
+            {
+                if (!res.OnlineBeatmapSetID.HasValue)
+                    return;
+
+                ShowBeatmapSet(res.OnlineBeatmapSetID.Value);
+            };
+
+            api.Queue(req);
+        }
+
         public void ShowBeatmapSet(int beatmapSetId)
         {
             // todo: display the overlay while we are loading here. we need to support setting BeatmapSet to null for this to work.