Add prompt to save beatmap on exiting editor

osu.Game/Screens/Edit/PromptForSaveDialog.cs

@@ -0,0 +1,33 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using osu.Framework.Graphics.Sprites;
+using osu.Game.Overlays.Dialog;
+
+namespace osu.Game.Screens.Edit
+{
+    public class PromptForSaveDialog : PopupDialog
+    {
+        public PromptForSaveDialog(Action exit, Action saveAndExit)
+        {
+            HeaderText = "Did you want to save your changes?";
+
+            Icon = FontAwesome.Regular.Save;
+
+            Buttons = new PopupDialogButton[]
+            {
+                new PopupDialogCancelButton
+                {
+                    Text = @"Save my masterpiece!",
+                    Action = saveAndExit
+                },
+                new PopupDialogOkButton
+                {
+                    Text = @"Forget all changes",
+                    Action = exit
+                },
+            };
+        }
+    }
+}