close chat tabs with middle mouse button

osu.Game/Overlays/Chat/Tabs/ChannelSelectorTabItem.cs

@@ -2,6 +2,7 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using osu.Framework.Allocation;
+using osu.Framework.Input.Events;
 using osu.Game.Graphics;
 using osu.Game.Online.Chat;
 
@@ -39,5 +40,7 @@ namespace osu.Game.Overlays.Chat.Tabs
                 Name = "+";
             }
         }
+
+        protected override bool OnMouseUp(MouseUpEvent e) => false;
     }
 }

osu.Game/Overlays/Chat/Tabs/ChannelTabItem.cs

@@ -16,6 +16,7 @@ using osu.Game.Graphics.Sprites;
 using osu.Game.Online.Chat;
 using osuTK;
 using osuTK.Graphics;
+using osuTK.Input;
 
 namespace osu.Game.Overlays.Chat.Tabs
 {
@@ -138,6 +139,17 @@ namespace osu.Game.Overlays.Chat.Tabs
             updateState();
         }
 
+        protected override bool OnMouseUp(MouseUpEvent e)
+        {
+            if (e.Button == MouseButton.Middle)
+            {
+                CloseButton.Action();
+                return true;
+            }
+
+            return false;
+        }
+
         [BackgroundDependencyLoader]
         private void load(OsuColour colours)
         {