Add simple download progress display to download buttons on playlist items

osu.Game/Graphics/UserInterface/GrayButton.cs

@@ -27,7 +27,7 @@ namespace osu.Game.Graphics.UserInterface
         [BackgroundDependencyLoader]
         private void load()
         {
-            Children = new Drawable[]
+            AddRange(new Drawable[]
             {
                 Background = new Box
                 {
@@ -42,7 +42,7 @@ namespace osu.Game.Graphics.UserInterface
                     Size = new Vector2(13),
                     Icon = icon,
                 },
-            };
+            });
         }
     }
 }

osu.Game/Overlays/BeatmapListing/Panels/BeatmapPanelDownloadButton.cs

@@ -37,6 +37,13 @@ namespace osu.Game.Overlays.BeatmapListing.Panels
                     RelativeSizeAxes = Axes.Both,
                 },
             };
+
+            button.Add(new DownloadProgressBar(beatmapSet)
+            {
+                Anchor = Anchor.BottomLeft,
+                Origin = Anchor.BottomLeft,
+                Depth = -1,
+            });
         }
 
         protected override void LoadComplete()