Debugger UI skeleton.

src/Xenia.Debug/Utilities/Changeable.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Xenia.Debug.Utilities {
+  public delegate void ChangedEventHandler();
+
+  public class Changeable {
+    private int changeDepth;
+    public event ChangedEventHandler Changed;
+
+    protected void BeginChanging() {
+      ++changeDepth;
+    }
+
+    protected void EndChanging() {
+      if (--changeDepth == 0) {
+        OnChanged();
+      }
+    }
+
+    protected void OnChanged() {
+      System.Diagnostics.Debug.Assert(changeDepth == 0);
+      if (Changed != null) {
+        Changed();
+      }
+    }
+  }
+}