Adding CancellationAsyncDisposable.

AsyncRx.NET/System.Reactive.Async.Disposables/System/Reactive/Disposables/CancellationAsyncDisposable.cs

@@ -0,0 +1,36 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information. 
+
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.Reactive.Disposables
+{
+    public sealed class CancellationAsyncDisposable : IAsyncDisposable
+    {
+        private readonly CancellationTokenSource _cts;
+
+        public CancellationAsyncDisposable()
+            : this(new CancellationTokenSource())
+        {
+        }
+
+        public CancellationAsyncDisposable(CancellationTokenSource cts)
+        {
+            if (cts == null)
+                throw new ArgumentNullException(nameof(cts));
+
+            _cts = cts;
+        }
+
+        public CancellationToken Token => _cts.Token;
+
+        public Task DisposeAsync()
+        {
+            _cts.Cancel();
+
+            return Task.CompletedTask;
+        }
+    }
+}