Imported Upstream version 5.10.0.47

Former-commit-id: d0813289fa2d35e1f8ed77530acb4fb1df441bc0

mcs/class/corlib/corert/Stream.cs

@@ -0,0 +1,28 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace System.IO
+{
+	partial class Stream
+	{
+		public virtual int Read (Span<byte> destination)
+		{
+			throw new NotImplementedException ();
+		}
+
+		public virtual void Write(ReadOnlySpan<byte> source)
+		{
+			throw new NotImplementedException ();
+		}
+
+		public virtual ValueTask<int> ReadAsync(Memory<byte> destination, CancellationToken cancellationToken = default(CancellationToken))
+		{
+			throw new NotImplementedException ();
+		}
+
+		public virtual Task WriteAsync(ReadOnlyMemory<byte> source, CancellationToken cancellationToken = default(CancellationToken))
+		{
+			throw new NotImplementedException ();
+		}
+	}
+}